♪♪ ♪♪ ♪♪ ♪♪ -Today on "America's Test Kitchen," Keith makes me roasted pork tenderloin with apples and shallots, Dan explains the science of stabilizers in whipped cream using bubbles, and Julia and I make a decadent gâteau invisible.

It's all coming up right here on "America's Test Kitchen."

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GreenPan Frost.

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♪♪ -Don't save those apples for your baking recipes.

Use them in your main course.

Today, we've got Keith here, and he's going to tell us about a fabulous meal that we can put together with pork and apples.

-Yeah, specifically pork tenderloin.

And pork and apples is a great combination.

You've seen them before.

So, let's start with prepping our apples.

-Okay.

-We're using three Golden Delicious apples here.

Firm when it's cooked.

Nice, sweet flavor that will balance out the pork.

-Good, buttery texture to it.

-Yeah, exactly.

-Yeah.

-So, I'm just going to take the core off here, peel off the top, peel off the bottom like so, and then just go in between.

Handy dandy apple corer.

Very easy.

So just line the hole up over the core.

Push down like that.

-Easy!

-And then I'll just take our other apples.

Now for our pork tenderloin.

These are about 16 ounces each.

Just a little bit of cleanup before we get into cooking.

There is this piece of silverskin on the top here.

That's what you want to get rid of.

When that sees heat, it will shrink up, and it will buckle.

-Sure.

-I have a boning knife here -- thin, flexible blade.

You can get underneath that silverskin really easy.

Start about halfway through.

Poke.

Now, at this point, I have the blade up slightly.

You don't want to turn it down like that, because you'll cut into the meat.

You actually want to cut up into the silverskin.

And you just pull it like that.

So, I'll take our pork.

Now, I just have this on a towel and want to make sure that we're really nice and dry here, and we're going to add some herbs to this.

-Okay.

-So I have 1 tablespoon of herbes de Provence.

So I'm just going to try to sprinkle this evenly all over the surface.

Now, this is kind of a nice ingredient, because you get a lot of different flavors in there.

-Yes.

-Now I have some table salt here, 1/2 teaspoon.

I'll sprinkle that over the pork, as well, and then 1/4 teaspoon of black pepper.

Once you have everything sprinkled, you can just roll the pork around.

That looks perfect.

So I'm just going to wash my hands, and then we can get to searing those.

-Okay.

♪♪ -So, we're going to end up roasting these pork tenderloins.

But since the pork is so small, it won't brown enough before it comes up to temperature.

-Gotcha.

-So we're going to give it a jump start.

So, I have a 12-inch skillet here with 2 tablespoons of olive oil over medium-high heat.

And I'm just going to set the pork in there.

I'm going to try to brown it on all sides.

2 minutes a side, so 8 to 10 minutes.

So, just going to keep an eye on that.

While that's happening, we have one more ingredient that I'm going to prep... -Okay.

-...which are shallots.

So, I have six shallots here.

Shallots are a great bridge ingredient.

-Mm-hmm.

-So they bridge between the savory pork and the sweet apples.

-Mm.

-So, as they cook, they become sweeter.

-Right.

-But they still retain some of that kind of allium pungency, which is kind of nice.

So, I have shallot here that's been peeled, and I'm just going to cut this crosswise into 1/2-inch-thick slices, so... Then I can just put those with his friends over here.

It's been 2 minutes, and we can check the first side of our pork... -Ooh!

-...which is absolutely gorgeous.

-Nice.

-Those look great.

I'm gonna try to get it browned on the other sides here, which will take 6 to 8 minutes.

-Okay.

-It's been 8 minutes, and you can see that we have nice browning over the entire surface of our pork.

-Beautiful.

-So I'm going to take this out.

I'm going to use that skillet here and all that beautiful fond in the skillet to cook our apples and shallots.

-Okay.

-So I'm going to add 2 tablespoons of olive oil.

I will add our apples to the pan and our six shallots.

-Mmm.

-Thank you.

I'm going to add just a little bit of granulated sugar here to help with browning.

-Oh.

-That's 1/2 teaspoon of sugar.

-Okay.

-So, I'm just going to turn the heat down to medium.

Stir that all around.

I'm going to cook this until the shallots and the apples start to soften a little bit, get a little bit of color on it, and then it'll be time to add our pork and the bacon.

But that will take 10 to 12 minutes for those to soften.

-Okay.

♪♪ -It's been 10 minutes, and you can see all this nice color that we've gotten on the apples and the shallots.

So I'm just going to shut the heat off here, and I'm going to take our pork and nestle that over the top... -Mmm!

-...of our apples and shallots.

Beautifully browned pork.

Now, if there are any juices on that plate, you want to add them back in.

Okay, so, now we've done the searing part, it's going to come to the roasting part.

So I have a 350-degree oven with the oven rack at the lowest position.

I'm going to put the pork in there.

We're going to go 15 to 20 minutes.

And what we're looking for is an internal temperature of 135 to 140 degrees.

So bringing that pork up nice and slow is the key here.

♪♪ It's been 15 minutes, so I should probably check on our pork.

So, what I'm looking for is 135 to 140 in the thickest part, so right -- -How we doing?

-136.

-I'll take it.

-So, I'm just going to take our pork out of here, put it onto a carving board.

So, I'm just going to take a piece of foil, tent our pork while it rests.

So, while that is resting, I'm going to take 1 tablespoon of unsalted butter, and I'm going to put that into our apple and shallot mixture.

And what I want to do is I want to use the residual heat in that skillet to incorporate that butter into any of the juices that are in there.

-Yes.

-I'm not looking for a sauce, per se.

What I want is that butter to melt, incorporate with whatever liquid is in there, glaze those apples and shallots.

Okay, so that's all incorporated.

Just going to set that aside.

We have a couple more minutes for our pork to rest, and then we can eat.

-Eat.

♪♪ -Pork has been resting for five minutes, but before I go any further, I want to add just a little bit of salt... ...and a little bit of pepper to our apples.

Stir that in to make sure that they are well seasoned.

For slicing our pork, I'm going to do 1/2-inch slices, and I like to do it on a bias.

You don't necessarily have to.

Just makes it a little bit prettier.

Perfect.

Look at that rosy interior.

-Lovely!

And this wasn't the pre-brined pork tenderloin, anyway.

It was all-natural and still nice and juicy.

-Yeah.

That's why you only cook it to 135, 140 degrees.

-Yes.

-That is the key step.

So... -All right, let's see those restaurant chops come back into play.

-[ Chuckles ] Couple more slices here.

-Lovely.

-Lovely.

-Can't forget the apples and shallots, though.

Très jolie.

[ Both laugh ] This is beautiful.

This is fine dining.

All right.

I have to tuck into the pork first.

Just on its own.

-Nice color.

Juicy.

-Gorgeous crust, as well.

Mmm.

That is what I would call softly seasoned.

It's beautiful.

Flavors are so soft, like the French countryside.

All right.

Going to get some apple.

-Mmm.

-Mmm.

-That's where everything comes together, doesn't it?

-Absolutely.

-Mmm.

-Get the sweetness of the apple, little bit of sweetness from the shallot, too.

-Mm-hmm.

-It browned and softened in there.

But that tartness that's coming through.

Keith, this was outstanding.

Little bit of French country brought to the home.

-Yeah.

On a Tuesday night.

-There you go.

Thanks so much.

Now, if it's a Tuesday night or any night of the week, if you want to make this at home, it starts by browning pork tenderloin on the stovetop, then sautéing apples and shallots.

Add the pork to the apple mixture and move it to the oven.

Add a little butter to the apples and shallots while the pork rests.

So, from "America's Test Kitchen," an absolutely lovely roasted pork tenderloin with apples and shallots.

♪♪ -Here I have two bowls of whipped cream.

This one looks great -- pillowy, fluffy, and delicious.

This one, however, looks pretty sad and deflated, and there's a pool of liquid cream underneath it.

So what's the difference?

Let's make some bubbles.

First, I'll make some with this solution in the green one.

As you can see, a beautiful bubble forms, but it pops basically instantly.

Now I want to make one with the solution in the blue tube.

Beautiful bubble.

But this one's different.

It actually...bounces?

Bet you've never seen that before.

Now, here's what's going on.

Both solutions contain soap and water, but this solution here has an added ingredient called glycerin.

Now, bubbles pop when water evaporates, leaving the bubble brittle and fragile.

Glycerin is what we call a humectant, meaning its molecules grab onto water and hold it in place.

The glycerin ensures the bubble remains flexible and elastic, like a soft balloon, instead of becoming a brittle shell.

24 hours ago, we whipped these bowls of heavy cream.

This one contains sugar, which, just like glycerin, bonds with the water to stabilize the bubbles.

This one, there's no sugar.

What's really cool about this is you don't need a ton of sugar to get this effect.

For whipped cream that stays whipped for hours, use 2 tablespoons of sugar for every 1 cup of heavy cream and then just whip, whip away.

♪♪ -Gâteau invisible is a gorgeous dessert with apples sliced paper thin stacked tall into a golden cake.

It looks really hard to make, but Bridget tells me it's surprisingly easy.

-Yes, and the invisible part of that refers to the fact that this is basically a cake of just apples and a little bit of a sort of pancake batter.

And the batter is so thin in comparison to the apples that it nearly disappears.

-Oh, I love it.

-Yeah.

We're going to start off with our batter here.

This is 2/3 cup of granulated sugar.

Now, we want to add some vanilla flavor in there, and we want to control the thickness of this batter, so we're going to avoid using a liquid vanilla.

Instead, we're going to use the potent vanilla bean.

And I just want to take a paring knife, go straight down here.

All right, so, I'm going to open this up just a little bit and then use the back of my paring knife to scrape out any of the seeds, the pulp that's on the inside there.

Now, it's not much of a batter without some eggs, so I've got two large eggs here.

Just want to whisk this together, and that's also going to help to loosen up those vanilla seeds in there.

-Mm-hmm.

-Nothing too complicated.

All right.

So, now our dry ingredients.

I have 1/2 cup of all-purpose flour and 1 teaspoon of baking powder, just a little bit of lift, and 1/2 teaspoon of table salt.

So, this gets whisked together, and you can see it's actually getting a little bit thick.

-Mm-hmm.

-This is by design, and I'll talk about that in just a minute.

But for right now, the batter is just whisked till it comes together.

-Well, that was easy.

-That's easy.

All right, so, I'm just going to put this aside for a moment.

-Mm-hmm.

-You bring down these apples.

Granny Smiths.

Can't go wrong here, and it's perfect for this cake for so many reasons.

These are tart and tangy.

I always say it's a half apple, half lemon in these.

-Mm-hmm.

-Super tart.

That's going to counter the sugar.

-Okay.

-Sweetness.

They have a lot of integrity, so they keep their shape even under a lot of cooking.

So, we're going to use -- This is 2 1/4 pounds of Granny Smith apples.

You can go up to 2 1/2 pounds.

And first thing you need to do is just peel them.

-Yep.

♪♪ -All right, Julia.

So, apples are all peeled.

-Mm-hmm.

-Next up is slicing.

And we're going to use a mandoline for this, because we found the perfect thickness of a slice of an apple is 1/10 inch.

-That's very thin.

-This is going to be really easy, super fast.

You just need to take a little care when you're using a mandoline.

-Mm-hmm.

-For some people, they might want to use one of these safety gloves.

-Yep.

-It's made of this fabric that's actually stronger than stainless steel.

All right, so, I'm going to glide the apple up and down here just until I get to the core.

-Okay.

-And, you know, the thing about using a mandoline -- Know where your fingers are.

-Yep.

-You can use a guard if you have that.

Just stop every once in a while, check and see if we're coming close to the core.

So you can see there, starting to get close to the core.

-Yep.

-Right there.

We're going to set a few aside, some of the pretty ones from the first side.

We're going to use that later on.

The rest goes right in here.

So now I just turn, rotate that apple 90 degrees, and do the same thing.

-Oh, the first side's the prettiest 'cause you have the whole apple to work with.

-That's exactly right.

All right.

So, there we go.

Apples all sliced.

-Nicely done.

-The 18 were set aside, the beautiful ones.

-Mm-hmm.

-All right.

The rest of them are going to come back over here to the batter.

Again, that batter is super thick.

-It really is.

-We're going to add in all of these apples.

And now I'm just going to gently toss them, start coating them with that batter.

So, I just want to get it well coated.

Doesn't have to be completely coated at this point, but just so that all the apples have a little bit of the batter on them.

Now I'm going to leave this to sit here for about 15 minutes.

That's why the batter was so thick.

There's a lot of juice in those apples, and 15 minutes will allow the juices to come out and thin the batter.

-Okay.

Nailing the consistency of the batter is really important in this recipe, because if it's too thick, it makes the cake taste a bit stodgy.

But if it's too thin, it doesn't stick to the apples, but will pool in the bottom of the pan.

Here's how we nailed the perfect consistency.

Most cake batters for this recipe contain sugar, flour, and eggs, along with some milk.

However, when apples are added to the batter, the consistency loosens.

Apples contain less sugar than the cake batter.

And because water is naturally drawn towards a higher concentration of sugar, osmosis draws water out of the apple cells.

So as the batter rests, the extra water from the apple oozes into the batter and dilutes it.

The batter now has a consistency that's too thin to coat the apples properly.

The solution is to start with an intentionally thick batter, which we achieve by omitting the milk.

When the sliced apples are added to this thicker batter, osmosis once again pulls the water into the batter, but this time, it thins it to the perfect consistency.

Now our batter pours smoothly and clings to every apple slice.

And that's why it's important to let the apples sit in the batter for at least 15 minutes.

-Definitely loosened up after that 15 minutes.

You can see how much more liquid-y that batter is.

-Yeah.

-All right.

So now we're about ready to assemble, and all I want to do at this point is kind of break up any clumps of apples.

I just want to make sure that every single slice in there is coated with this batter.

All right.

So now it's time for our pan.

This is a 1-pound loaf pan.

It's 8 1/2 inches long, 4 1/2 inches wide, and 2 3/4 inches tall.

We've greased it, lined it with an 8x12-inch piece of parchment, and then greased the parchment.

-Okay.

-All right.

So, with all that being said, let's start adding our apples to the pan.

So we're going to work with about 1/4 cup of apples at a time.

And I just want to make sure that I'm allowing the batter to drip back down into the bowl.

-Yeah, I notice you're using a slotted spoon.

-Yes.

So I've got my slotted spoon here, and I'm just going to start -- It's okay if some of the apples are folded over on each other.

Just going to start adding them to the bottom here.

Now I've got this first layer in there, I just want to take a spoon, kind of push down just a little bit, get any gaps.

If I find any gaps, I can always add an apple.

I'm going to put an apple right in there.

All right, and then continue with more of the apples.

So I'll just keep doing this, about 1/4 cup per spoonful, pressing down just a little bit... -Mm-hmm.

-...and continue.

♪♪ All right.

I think that is it for the apples.

We're going to press on the top here pretty firmly at this point.

We want no air pockets in here.

So that is good.

Nice and compact.

-Mm-hmm.

-We've got a few tablespoons of batter left here.

That's on purpose, because we're going to take our pretty slices.

So I'm just going to dip this right in there, one side.

Going to get a little messy.

That's totally fine.

-Mm-hmm.

-And we're going to start to shingle this right on top.

-Just one-sided?

-Just one side.

There's going to be a little bit of batter left over, but don't worry about it.

-Ah.

Gotcha.

-So, we do want to make sure that one side has a little bit of batter, and that's going to be the side that we place down.

-Okay.

-All right.

So it was 18 slices.

-Mm-hmm.

-So it's going to be six rows.

We're going to shingle across but also shingle down.

-Gotcha.

-So... -Shingle, shingle.

-Shingle, shingle.

♪♪ All right.

How's this looking, Julia?

-It looks gorgeous.

-Last one here.

Now I want to go back.

-Mm-hmm.

-Get this nice and even, pretty firmly at this point.

And now we're not going to waste this little bit of batter in here.

I'm going to pour this over the top and then spread it out evenly.

All right, so, let me tell you about our oven setup.

We've got two racks.

One is set to the middle position where we're going to put our cake.

-Mm-hmm.

-And one is set lower than that with a sheet pan right on it to collect drips.

-Makes sense.

-Yes.

And we've got a little piece of parchment on there, as well, for easy cleanup.

-Mm-hmm.

Now this is going to go into the 350-degree oven for at least an hour and a half... -Wow.

-...up to 1 3/4 hours.

Yeah, it's a really deep cake, but it's a relatively low temperature, so it can withstand it.

But we're going to leave it in there until the top is really beautiful deep brown.

♪♪ Beautiful.

This was in there for about an hour and a half, but I do want to check to see if it's done all the way through.

And you just take a skewer.

Should go in and out, no problems at all.

One last thing that we need to do is just run a paring knife on either side.

We don't need to do it to the two long sides with the parchment.

Just releasing the sides before the sugar has a chance to cool and set.

One last thing, a little adornment.

It's so French.

This is 2 teaspoons of apple jelly.

-Oh, yeah.

-Just melt it in the microwave for a few seconds and then brush this on top.

Let it glisten.

-Mm-hmm.

-Gorgeous.

Now it looks like it's straight out of a pâtissière.

-It really does.

-Yes.

-It's amazing what just a little gloss does, huh?

-Yeah, it's words to live by.

-[ Chuckles ] -All right.

So, we're going to leave this in the pan, let it set up.

If we were to turn this out now, it would be like scalloped potatoes -- loose, right?

-Gotcha.

-Just loose all over the counter.

So we're going to let it set up for a little bit, about an hour and a half.

-Okay.

♪♪ -All right.

It's been 90 minutes.

It's set up just enough.

You can see it did deflate a little.

I'm going to gently pull it up.

-Oh, wow.

-There we go.

Flatten this out, and I'm going to let it cool completely at this point.

I know.

It's kind of amazing.

-You have to bend over and look at it from the side.

It's incredible.

You see the individual layers of apple, and you'd think that took hours for you to assemble.

-Uh-huh.

Uh-huh.

-I watched you.

-Yeah.

-It took you a second.

-You know the truth.

-[ Chuckles ] -So, we're going to let this cool completely.

That's going to take about two hours.

-Okay.

-One last thing that we want to do is add a little whipped cream.

-Mm-hmm.

-Totally optional, but actually not.

-[ Laughs ] -Definitely need to make this.

So, it's just 1 cup of heavy cream, well chilled, 'cause that's going to whip up much better.

All right.

2 tablespoons of packed dark brown sugar.

-Ooh, brown sugar.

-And just a little bit of cinnamon.

This is 1/4 teaspoon of ground cinnamon.

-Oh, I like it.

-All right.

I'm going to attach the whisk, here, attachment.

And then I'm going to start this on medium-low speed, just so it doesn't splatter everywhere, until it gets foamy.

That's going to take about a minute.

♪♪ All right.

It's been a minute.

Nice and foamy.

Now I'm going to crank it up to high and let it go until it's soft peaks.

Depending on the heavy cream, that might take a minute or up to three minutes.

♪♪ See how it's just going right over on the tip end?

-Yeah.

-That means it's nice soft peaks.

Into a nice, little serving bowl so we can attend our fancy tea party here.

-Mm.

-All right.

-Look at that.

-Isn't this beautiful?

-It's just stunning.

-Wait till you see inside.

-Oh.

That's where the layers really show up.

So, we're going to cut this into six wedges.

All right.

-All right.

I've got to see the inside of this.

-All right.

Let me show you.

Would you like this end peace, Julia?

-Sure.

I won't say no.

Oh, goodness.

It really does look like you painstakingly did each piece of apple on its own.

-All right, so, a little bit of cream.

-Oh, yeah, your fancy whipped cream.

-Would you like it on the side?

-Right on top.

-Right on top.

-Oh, thank you.

-Big mound.

-Mmm.

Oh, yeah.

-All right.

-I'm going in.

-Please do.

And you get that little end piece that has that bit of toffee kind of caramelized apple.

Yeah.

You won the lottery.

-That is like the best part of an apple pie.

-Yes.

Isn't it?

-Uh, ye-- That is incred-- That is incredible.

-Incroyable.

-It is.

The apple flavor is so pure.

-Yes.

-I really like the egg mixture.

You get a little bit of vanilla, but it is by no means overpowering.

-No.

-It's just a hint.

-Yes.

No, definitely.

I mean, it's technically called a cake... -Yeah.

-...because we put flour in it, basically.

-Right.

-But look at this.

It's just being held together by that little bit of batter that's gone invisible.

-Bridget, this is spectacular.

I love it.

Thank you for showing me how to make it.

-D'accord.

-If you want to make this irresistible apple dessert, start by slicing Granny Smith apples very thinly using a mandoline.

Let the apples release their liquid into the batter, then bake and cool the gâteau in a loaf pan.

From "America's Test Kitchen," an incredible recipe for gâteau invisible.

You can find this recipe and all the recipes from this season, along with select episodes and our product reviews, at our website, americastestkitchen.com/tv.

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GreenPan Frost.

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