Triple Chocolate Mousse Cake

Happy May long weekend! I decided to try something which I considered a little trickier last week, seeing as this was a long weekend approaching, and I had a bit of time on my hands. I honestly thought that this would be difficult to make, but in fact it was just a lot of little easy steps that turn out into something so fabulous looking. And what else surprised me, is that I had everything in my pantry, so there are no special ingredients required.

Give yourself some time to make it though, I made the cake base one day and then the next day I finished it off with the mousses. So, I started it Thursday night after work and then finished it Friday night. It's now Sunday and I am still enjoying it, piece by piece. I am keeping it refrigerated.


Triple Chocolate Mousse Cake
From Cooks Illustrated (recipe the same, but with a different technique - my own notes are in italics)

Makes one 10" cake, serves 12-16

Bottom Layer
90g unsalted butter, plus extra for greasing pan
200g bittersweet chocolate, chopped fine
3/4 teaspoon instant espresso powder
1 & 1/2 teaspoons vanilla extract
4 large eggs, separated
pinch salt
1/3 cup packed light brown sugar, crumbled to remove lumps (this is an important step)


Middle Layer
2 tablespoons Dutch processed cocoa powder, sifted
5 tablespoons hot water
200g bittersweet chocolate, chopped fine
1 & 1/2 cups cold heavy cream
1 tablespoon white sugar
1/8 teaspoon salt

Top Layer
3/4 teaspoon powdered gelatin
1 tablespoon water
170g white chocolate (chips or chopped finely)
1 & 1/2 cups cold heavy cream

To make bottom layer:
Preheat oven to 325F. Butter bottom and sides of pan with 9.5" spring form pan (I had 10" so went with that and I also lined my base with parchment. The first time I made this cake I couldn't remove the cake from the base once it was cooked). Melt butter, chocolate and espresso powder in large heatproof bowl set over saucepan 1" with simmering water, stirring occasionally until smooth. Remove from heat and cool mixture for 5 minutes. Whisk in vanilla and egg yolks.

In stand mixer fitted with whisk attachment, beat egg whites and salt at medium speed until frothy, about 30 seconds. Add half of brown sugar and beat until combined, about 15 seconds. Add remaining brown sugar and beat at high speed until soft peaks form when whisk is lifted, about 1 minute longer, scraping down the sides halfway through. Using whisk, fold one-third of the beaten egg whites into chocolate mixture to lighten. Using rubber spatula, fold in remaining egg whites until no white streaks remain. Carefully transfer batter to prepared spring form pan, gently smoothing top with offset spatula.

Bake until cake has risen, is firm around the edges, and center has just set but is still soft (center of cake will spring back after pressing gently with finger), 13 to 18 minutes. Transfer cake to wire rack to cool completely. Cake will collapse as it cools. Do not remove cake from pan as it cools. OK, so after it cooled, I did remove it from the pan (as well as remove the parchment) and placed it onto a cake board, then placed the ring part of the pan back around the cake, ready for the mousses. In my first trial run, after I had followed the recipe to a tee, I couldn't remove the base of the pan from the cake. It was fine because I was serving it to my friends and family - they LOVE all the rejects :) , but I really didn't want the base "leftover" as I cut away the cake. It's a personal choice for presentation. If you are not worried about this, then just follow the recipe - I guarantee it will be delicious!)

For the middle layer: Because I wanted a really sharp edge on my cake, I lined the ring with a strip of parchment paper. I found that using a small palette knife to loosen the cake gave a rough edge, the parchment just peeled away.

Combine cocoa powder with hot water in a small bowl; set aside. Melt the chocolate in large heatproof bowl set over saucepan with 1" simmering water, stirring occasionally until smooth. Remove from heat and cool slightly, about 5 minutes.

In clean bowl of stand mixer fitted with whisk attachment, whip cream, white sugar and salt at medium speed until mixture begins to thicken, about 30 seconds. Increase speed to high and whip until soft peaks form when whisk is lifted, about 1 minute.

Whisk cocoa powder mixture into melted chocolate until smooth. Using whisk, fold in one-third of whipped cream into chocolate mixture to lighten. Using rubber spatula, fold in remaining whipped cream until no white streaks remain. Spoon mousse into spring form pan (if you removed the base, carefully smooth mousse over cake, holding ring part of pan centered over cake base, and pressing firmly to ensure no mousse escapes through the bottom) and tap gently on counter three times to remove any large air bubbles (be careful here if you have removed the base); gently smooth top with offset spatula. Wipe inside of pan to remove any drips. Refrigerate cake at least 15 minutes while preparing the top layer.

For the top layer: In a small bowl, sprinkle gelatin over water, let stand at least 5 minutes. Place white chocolate in medium bowl. Bring 1/2 cup cream to simmer in small saucepan. Remove from heat, add gelatin mixture and stir until fully dissolved. Pour cream mixture over white chocolate and whisk until chocolate is melted and mixture is smooth, about 30 seconds. Cool to room temperature, stirring occasionally, 5 to 8 minutes (mixture will thicken slightly).

In clean bowl of stand mixture fitted with whisk attachment, whip remaining cup of cream at medium speed until it begins to thicken, about 30 seconds. Increase speed to high and whip until soft peaks form when whisk is lifted, about 1 minute more. Using whisk, fold one-third of whipped cream into white chocolate mixture to lighten. Using rubber spatula, fold remaining whipped cream into white chocolate mixture until no white streaks remain. Spoon white chocolate mousse into pan over middle layer. Smooth top with an offset spatula. Return cake to refrigerator and chill until set, at least 2.5 hours.

To remove cake from pan, run knife around edges to loosen cake from pan, then release the ring and lift up. If you lined the ring with parchment, you can just release the ring and peel away the parchment.

Garnish cake before removing from the pan, so that none of your decoration runs down the sides - unless this is the look you are going for!  You could dust with cocoa powder or chocolate curls, I just striped (I am sure there's a technical name for this effect) chocolate ganache over the top - half melted chocolate half cream, melted and then leave to cool to desired thickness before "striping" in a pastry bag fitted with a small plain tip.

Oh, and use a hot clean knife to cut perfect slices. Cooks Illustrated recommends using a cheese wire, which sounds great, but I don't have any on hand - so I resorted to my trusty chefs knife.

Enjoy!