Bittersweet Chocolate Mousse Cake

Bittersweet Chocolate Mousse Cake
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bittersweet chocolate mousse cake
Very chocolatey!

Wow! Just the name sounds like creamy clouds of chocoliciousness. If this is anything like it sounds, it will be the Holy Grail of chocolate desserts. Let’s see. Chocolate for super flavor: check. Mousse for light-as- air creaminess: check. Cake, so that everything holds together: check. See, what did we tell you? It’s possible the Holy Grail awaits.

We saw this in The Science of Good Cooking, by the Editors of Cook’s Illustrated. Sounds as if it might be a scientific recipe. Maybe you need a lab coat and beakers full of bubbling liquids to make this. Nope. It’s actually pretty easy; no lab coats required, and bubbling beakers are optional.

In reality, we were doing this recipe as a trial run for part of a pot luck dinner that’s coming up, where we committed to making a dessert. We’d hate to bring an untested recipe to a pot luck. Sure, it’s chocolate, so people will eat it. But, is it the best we can do? Besides, if it is really good, people at the pot luck will eat it, and you’ll be a bit too polite to take a big slab for yourself. Yep, the best solution is to do a trial run and eat it all yourself. (This is actually a scaled-down version of the original, which is double in size and makes a 9-inch cake.)

Just because this recipe uses a bain-marie doesn’t mean it’s difficult. And, if you’re going to be scratchin’, you’ll use one sooner or later. Might as well be with something chocolate. And, we’ll help with lots of baby steps in the instructions. So, read through them, take a deep breath, and we’ll get through this together.

Makes one 6-inch cake.

Bittersweet Chocolate Mousse Cake

Bittersweet Chocolate Mousse Cake


  • 6 Tbs unsalted butter, chopped into pieces
  • 6 ounces bittersweet chocolate, chopped
  • 1/2 ounce unsweetened chocolate, chopped
  • 4 large eggs, separated
  • 2 tsp vanilla extract
  • Pinch salt
  • 1/3 cup packed (66 grams) light brown sugar, broken up after packing

Abbreviated Instructions

Preheat oven to 325°F

Butter a 6-inch springform pan. Line bottom with baking parchment. Butter parchment. Flour pan. Wrap bottom and sides with large piece of aluminum foil.

Place chocolate and butter in a heat proof bowl over simmering water. Stir occasionally, until melted and smooth. Remove from heat and let cool slightly. Whisk in egg yolks and vanilla. Set aside.

Using a mixer, whip egg whites and salt until foamy, about 30 seconds. Add 1/2 of the sugar and whip until mixed and foamy, about 30 seconds. Add remaining sugar and whip on high until firm peaks form, about 2 minutes.

With whisk, stir about 1/4 of egg whites into the chocolate mixture. Fold in remaining egg whites in two additions.

Scrape into prepared springform pan. Place pan in baking dish, and pour simmering water around to form a water bath to a depth of about one inch.

Bake for 40-45 minutes, or until top is set and internal temperature is about 170°F.

Remove from water bath. Remove foil and let cool about 10 minutes. Run knife around edge and let cool 2 hours. Wrap in plastic and refrigerate overnight.

Remove sides of springform pan. Use a spatula to lift cake, carefully remove baking parchment, and place on plate.

Ingredient discussion:

Only a few ingredients can only mean one thing: use the best you can. For us, that meant Callebaut chocolate, farm fresh free-range eggs, and home-made vanilla extract. Since chocolate, especially good chocolate, is pretty pricey, we order in bulk about once a year. Sure, it can seem like a serious outlay all at once, but if it lasts a year, and you get really good chocolate, it’s a bargain.

Procedure in detail:

prepared springform pan
Butter, line with parchment, butter, flour, shake out excess, and your pan is ready.

Prepare pan. Using slightly warmed butter, grease your springform pan on the bottom and the sides. Now, cut a circle of parchment for the bottom. We fold a piece of parchment in half diagonally (so you have a triangle), then in half again (still a triangle), and again, and again (now a skinny triangle; as if you folded a pizza along the cuts between the slices), and measure and cut off the edge. Unfold paper and you have a circle. Place that on the bottom of the pan, and butter. Now, flour the pan by putting in about a tablespoon of flour and shaking it around so the bottom and sides are coated. Rap on the upside-down pan to remove excess flour. Now, wrap the outside in aluminum foil (all springforms leak, and you’ll be setting this in the water bath). Whew. That’s a long explanation. It’s not that bad. Just remember: chocolate.

Preheat oven to 325°F. And place a rack in the lower middle of the oven.

separating eggs
Separate the eggs into small bowls one at a time, emptying the whites between eggs, so if a yolk breaks, you’ve only one egg you need to set aside because of yolk contamination.

Separate eggs. The key is not to get yolks in with the whites, so we separate the eggs while cold one at a time into two small bowls. Once one egg is separated, we add the white to a clean mixing bowl. That way, if we break a yolk, we only have egg yolk in the white of one egg, and, we can set that aside for another use. Using cold eggs makes the yolks less likely to break, too. Don’t worry. You can do it.



melting chocolate
Here’s our chocolate melting set-up. If we didn’t need the hot water later, we would have melted it in the microwave (50% power; 30- second increments).

Melt chocolate and butter. Chop up the chocolate with a chef’s knife and place in a heat- proof bowl. Add the pieces of butter and place bowl over a pan containing water. Place over medium heat and let the water simmer. Be careful that you don’t get water in the chocolate. Use a whisk to stir butter and chocolate around until smooth and melted. Remove from heat.



whisking in egg yolks.
Whisking in the yolks and vanilla will make the chocolate thicken up considerably.

Whisk in yolks. Let the chocolate cool for a few minutes, then whisk in the egg yolks and the vanilla. The chocolate will thicken up a bit as the yolks mix in. Set aside.



Whip whites and salt. For some reason, this always seems a bit tricky. It’s not. You need to have a clean bowl (no trace of oil), and a mixer that goes fast. After separating the eggs, the whites should have ended up in the mixer bowl. Now, add your pinch of salt, and whip until just foamy, about 30 seconds.

Add half of the sugar. Add about half the brown sugar to the whites, and whip on high until thoroughly mixed and foamy, about 30 seconds.

whipping egg whites
Add the sugar in two parts before whipping the whites to soft peaks. This will help ensure that the sugar is completely dissolved.

Add remaining sugar. Dump in the remaining sugar, and whip on high until the egg whites form stiff peaks, about 2 minutes. To check, we just turn off the mixer and tilt it up. If the whites form a nice peak that doesn’t sag, we’re good to go. Otherwise more whipping is required.



stirring in egg whites
Stir in the first portion of the egg whites to lighten the batter, then fold in the rest in two additions.

Fold in egg whites. Okay, now’s the tricky part — but not too tricky — we’re going to fold the whites into the chocolate. This is done in three parts. Scoop about 1/4 of the egg whites onto the chocolate. Stir this in with the whisk. The chocolate should now be a bit lighter. Scoop in 1/2 of the remaining whites, scoop the chocolate from the bottom of the bowl up and over the whites, and then push this chocolate through the whites. Do this again and again, just until the batter no longer has egg white streaks. Now, the batter should seem fluffy. Repeat with the remaining egg whites, but complete the folding with a rubber spatula.



mousse cake batter
A few more folds and this batter will be ready for the pan.



batter in the prepared pan
Scrape the batter into the pan. Then, if you want, lick the bowl. Chef’s prerogative.

Pour into prepared pan. Scrape the batter into the prepared pan and place the springform pan wrapped in aluminum foil into an 8×8″ baking pan.



water bath
Ready for the water. Batter in pan in foil that will be in the water in another pan.

Add simmering water. Pour the water that you used for melting the chocolate into the baking pan to a depth of about 1 inch. This is your bain marie, or water bath.


Bake. Carefully place the water bath in the oven, and bake for about 40 to 45 minutes, or until the top is set and the internal temperature is around 170°F. We did use an instant read thermometer for this, but, it also appeared that a toothpick inserted into the center might come out clean — the thermometer did.

mousse cake
Right out of the oven. For the lightest texture you want to let this cool slowly so it doesn’t collapse.

Cool. Once baked, remove from the water bath and remove the foil. Set on a rack and allow to cool for 10 to 20 minutes, then run a knife around the edge to loosen. Do not remove pan at this time. Instead, allow the cake to cool to room temperature (several hours), then wrap, still in pan, in plastic wrap and refrigerate overnight.


Plate. Run a knife around the cake again and loosen sides of the springform pan. Lift off carefully.  Now, use a thin, wide spatula to lift cake from the bottom of the pan. Gently cradle cake in one hand, and remove parchment from the bottom (If you were making a 9-inch cake, you might have to invert it onto another plate before removing parchment). Place on cake dish.

bittersweet chocolate mousse cake
Very chocolatey! Bittersweet Chocolate Mousse cake.

Serve. Use a sharp knife to slice. (It may help to warm the knife with hot tap water and dry between cuts)

Whew! That wasn’t so bad. How is it? While it’s really good, it isn’t exactly what we were hoping for as it is just a bit on the dry side, and isn’t quite as intensely chocolatey as we’d hoped. Those two things would have been okay, if the cake were even a little lighter in texture. A bit more ethereal, or more like biting into a cloud. Instead, it is rather like a smooth cheesecake, denser than we had hoped. Maybe an extra egg white or two would be enough to move this up to the five-star category, but for now it’s only four stars. As for the people at the pot luck, let them eat carrot cake!

Worth the trouble?

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