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Chocolate Mousse Layer Cake

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Serves twelve.

Yields one 9-inch cake.

The simplest way to decorate this cake is to press chopped, toasted walnuts onto the sides. For a more dramatic look, try wrapping the cake in a chocolate band (see our video for how-tos) and topping it with white chocolate curls.

For the chocolate cake:
  • Vegetable oil or pan spray for the pan
  • Flour for the pans
  • 6 oz. (1-1/2 cups) cake flour
  • 1 oz. (6 Tbs.) unsweetened natural cocoa powder
  • 2 tsp. baking powder
  • 1/4 tsp. baking soda
  • 1/4 tsp. table salt
  • 1 cup granulated sugar
  • 1/4 cup vegetable oil
  • 1 large egg
  • 2 tsp. pure vanilla extract
  • 1 cup water
For the mousse:
  • 2 cups heavy cream 
  • 3/4 oz. (1/4 cup) unsweetened natural cocoa powder
  • 13 oz. bittersweet chocolate, chopped
  • 4 oz. (1/2 cup) unsalted butter, at room temperature and cut into small pieces
  • 2 tsp. pure vanilla extract or 1 to 2 Tbs. brandy or Cointreau
  • Pinch table salt
  • 7 large egg whites, at room temperature
  • 1/2 cup granulated sugar
Tip:
If you’re concerned about uncooked egg whites, you can use a pasteurized egg white product like Just Whites. 
For decorating the cake:
  • 7 oz. (1-1/2 cups) walnut halves, toasted chopped medium-fine
  • OR 6 oz. bittersweet chocolate, plus a 10- to 12-oz block of bittersweet, semisweet, milk or white chocolate
Make the cake:

Position a rack in the center of the oven and heat the oven to 325°F. Lightly grease a 9x2-inch round cake pan, line the bottom with parchment, and flour the sides (but not the bottom).

Sift the cake flour, cocoa powder, baking powder, baking soda, and salt into a large bowl. Add the sugar and whisk until well blended. Measure the oil into a 1-cup liquid measure, add the egg and vanilla, and mix with a fork to blend. Add the egg-oil mixture to the dry ingredients and then add the water. Whisk until the dry ingredients are just moist, about 1 minute, scraping down the sides of the bowl. Pour the batter into the prepared pan.

Bake until a pick inserted into the center of the cake comes out clean, 32 to 34 minutes. Let cool on a rack for 20 minutes. Lightly grease a wire rack, invert the cake onto it, lift off the pan, peel off the paper, and let the cake cool completely.

Make the mousse:

Set up an ice bath by partially filling a large bowl with cold water and some ice.

Combine the cream and cocoa in a large saucepan set over medium heat. Bring to a full boil, whisking occasionally to blend in the cocoa. Slide the pan off the heat and immediately add the chopped chocolate and the butter; whisk slowly until melted and smooth.

Scrape the chocolate mixture into a large bowl. Add the vanilla and salt. Set over the ice bath and stir constantly with a rubber spatula, scraping the sides very frequently, until the chocolate cools to room temperature (don’t stop stirring or lumps will form) Remove the bowl from the ice bath.

Put the whites in a large clean bowl. Whip with an electric mixer on medium-low speed until very foamy. Increase the speed to medium high and beat until the whites form very loose, soft peaks. Slowly add the sugar. Continue beating until the whites are shiny and form floppy peaks.

Working quickly, scoop about a third of the whites into the cooled chocolate mixture and fold together with a rubber spatula or a whisk until blended. Scrape the remaining whites into the chocolate and fold together gently but thoroughly. Scoop out about 1 cup of the mousse into a bowl, cover, and refrigerate for finishing touchups. Use the rest of the mousse to assemble the cake.

To assemble the cake:

Set the ring of a 9-inch springform pan on a large, flat cake plate. To cut the cake into layers, it helps if the cake is slightly chilled. Set the cake bottom side up on a parchment-lined work surface. Cut into three equal layers. Set aside without separating the layers.

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Gently flip the top cake layer (really the bottom) upside down and center it in the  springform ring so the mousse can flow over the edge to frost the sides; handle the cake carefully (if it breaks, just piece it together). Scoop about one-third of the mousse (a heaping 2 cups) onto the cake layer in the ring and gently spread to cover. Flip the next cake layer (the center) on top of the mousse and press gently to level it, if necessary. Scoop half of the remaining mousse over the layer and spread gently. Flip the remaining cake layer upside down and set it on top of the mousse. Press gently to level it. Spread on the remaining mousse and smooth the top; the cake should fill the ring (don’t worry if a little mousse leaks out of the bottom).

If you’re decorating the cake with nuts, add enough mousse to the top layer of the cake so it comes to the rim of the springform ring. Smooth the top with a metal spatula or the flat, straight edge of a long knife. Pull an icing comb or a long serrated knife across the mousse, making a wavy pattern. If the pattern doesn't hold, pop the cake in the fridge for 5- to 10-minute intervals so the mousse starts to set, and then try again. (If you're wrapping the cake with a chocolate band, skip this step) Put the cake in the fridge for at least 6 hours and up to 24.

To decorate:

Take the cake from the fridge. Run a long, thin knife or metal spatula under hot water and dry it well. Slide the warm knife between the cake and the ring, pressing the knife against the ring, to loosen the cake. Carefully release the springform clasp; gently pry it all the way open. Lift off the ring and clean the plate edge. If you’re decorating the cake with nuts, mold strips of foil around the cake plate to keep it clean.

If the cake’s sides have bare patches, use a small metal spatula to touch them up with some of the reserved mousse. Chill the cake.

To decorate with nuts: Scoop up a handful of the walnuts in one hand and pat them onto the side of the cake. Many will fall off but you'll be left with a single layer of nuts. Repeat, rotating the cake to cover all the sides.

To decorate with a chocolate band, follow the method demonstrated in the video.

Once decorated, keep the cake refrigerated and serve it within 8 hours. Remove from the fridge 10 to 15 minutes before serving.

Photo: Scott Phillips



This cake was not easy to make, but with careful planning and enough time it's doable. I made the cake in the morning on day 1, and let it cool until late afternoon. It didn't rise as much as I had hoped, and it also was domed which made it difficult to cut into three layers but I managed to do it, just. The mousse went well and was delicious. I assembled the cake and put it in the fridge overnight to set. The next morning I made the chocolate band. You definitely need to watch it carefully as I let mine set up a bit too much so I couldn't ruffle it as much on the top as I should have without it cracking. Instead of chocolate curls on top, I sprinkled edible gold flakes. As I had made sure to smooth the mousse on top very carefully, it looked great and together with the chocolate band it looked really impressive! Taste-wise, I'd give the mousse an 8 or 9 as it wasn't very complex in flavour, but the cake itself was a bit dry. There was enough mousse that it didn't really matter, but still, I would've liked it better had the cake been more moist.

I have been making and decorating cakes for a few years but this was the first time i ever made mousse. You really need to set up your work space ahead of time, the cold water bath, the beaters, warm up your eggs, etc. Do as much prep work as possible before starting, otherwise you will be yelling for help at a crucial moment like I did. First try, my eggs wouldn't fluff so I read that you should make the eggs room temp, not get ANY yolk in the whites, etc. I started over and they it was perfect. This was not a simple recipe, but now that I have done it once, I know how to do it and it will seem way easier next time around. This is a great option to do in lieu of chocolate ganache which uses way more actual chocolate and cream and is pricier. I also decorated mine with chocolate curls on the sides, and huge, fresh strawberries on top which I drizzles with chocolate. All that said, this was THE best tasting cake I have ever made. It was the perfect texture, sweetness, presentation, etc. I can't say enough good about it. Highly recommended and well worth trying to figure out how to do it.

I have made this cake a few times using the chocolate curls method to decorate it. It looked beautiful, like from a bakery and my guests loved it. I have also made the mousse seperately to use for other recipes or just to have the mousse which is a good recipe in itself. As some of the other reviewers mentioned I also only cut it into two layers, it was still nice, just not as tall. Three layers looks pretty tricky, but I will give it a try one of these days when I am feeling braver! I have Abigail Dodge's cookbook and always really enjoy her recipes, they are creative and impressive, but not too much for the home baker to manage.

This cake is amazing. Definitely worth the work. I have found if you decorate with a chocolate band with white chocolate curls, using a knife warmed by sink water, slices right through the chocolate and you dont run in to problems with the shattered band.

This cake was indeed impressive and very easy to make, given a little planning. I only cut the cake into 2 layers but after watching the video on this website on how to cut a cake into layers, I'll definitely try 3 layers next time. The mousse itself is delicious, worth making on its own.

OMG... this is the best cake ever. We coat the sides with chopped walnuts and make semi sweet chocolate curls for the top. We also make it with 2 layers (it's easier). Definitely a show stopper.

I've been making this cake for a few years now. It is not a project that one undertakes lightly, but it isn't terribly tricky. The cake is certainly a show-stopper. I have always used the chocolate band and the white-chocolate curls to finish the cake and it makes quite an impression. Add some very tall gold birthday candles and you have a cake to remember. It is rich and delicious and worth the effort and the calories, too. The only difficulty is in the slicing. In my hands, the chocolate band tends to shatter and be kind of a mess by the time it hits the plates. People never seem to mind, though!

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