Triple Chocolate Mousse Cake

I have always wanted to try this cake. It contains no wheat and since Alan is avoiding wheat these days, it was the perfect choice for his birthday cake. And what a treat it was! By the time I got around to taking a few pictures of it, there was very little left. This was a recipe that I have had in my scrapbooks for a while now, cut out of an old "Cook's Illustrated" magazine. You can always trust those hard-working Cook's Illustrated people.

 
Triple Chocolate Mousse Cake
Serves 12

Bottom Layer:
6 Tbsp butter, cut into 6 pieces, plus extra for greasing the pan
7 ounces bittersweet chocolate, chopped fine
3/4 tsp instant coffee or instant espresso powder
1 1/2 tsp pure vanilla extract
4 large eggs, separated
Pinch fine sea salt
1/3 cup packed brown sugar, lumps removed with your fingers

For the bottom layer: Preheat the oven to 325F. Butter the bottom and sides of a 9-inch springform pan. Melt butter, chocolate, and coffee powder in large heatproof bowl set over saucepan filled with 1 inch of barely simmering water, stirring occasionally until smooth.
Remove from heat and cool mixture slightly, about 5 minutes. Whisk in the vanilla and egg yolks; set aside.
In a stand mixer fitted with the 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 the whisk is lifted, about 1 minute longer, scraping down sides halfway through. Using whisk, fold one-third of beaten egg whites into chocolate mixture to lighten. Using rubber spatula, fold in the remaining egg whites until no white streaks remain. Carefully transfer batter to prepared pan, gently smoothing top with offset spatula.
Bake until cake has risen, is firm around the edges, and centre has just set but is still soft (centre of the cake will spring back after pressing gently with finger), 13-18 minutes. Transfer cake to wire rack to cool completely, about 1 hour. (Cake will collapse and shrink as it cools and this is fine). Do not remove the cake from pan.

Middle Layer:
2 Tbsp cocoa powder
5 Tbsp hot water
7 ounces bittersweet chocolate, chopped fine
1 1/2 cups cold heavy cream
1 Tbsp granulated sugar
1/8 tsp fine sea salt

For the middle layer: Combine the cocoa powder and hot water in small bowl; set aside. Melt chocolate in large heatproof bowl set over saucepan filled with 1 inch of barely simmering water, stirring occasionally until smooth. Remove from heat and cool slightly, 2-5 minutes.
In clean bowl of a stand mixer fitted with whisk attachment, whip cream, granulated 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, 15-60 seconds.
Whisk cocoa powder mixture into melted chocolate until smooth. Using whisk, fold 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 springform pan over cooled cake and gently tap pan on counter 3 times to remove any large air bubbles; gently smooth top with offset spatula. Wipe inside edge of pan with damp cloth to remove any drips. Refrigerate cake at least 15 minutes while preparing top layer.

Top Layer:
3/4 tsp powdered gelatin
1 Tbsp water
6 ounces white chocolate, finely chopped
1 1/2 cups cold heavy cream

For the top layer: In 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 over medium-high heat. 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, 5-8 minutes (mixture will slightly thicken).
In clean bowl of stand mixer fitted with whisk attachment, whip remaining cup cream at medium speed until it begins to thicken, about 30 seconds. Increase speed to gigh and whip until soft peaks form when whisk is lifted, 15 to 60 seconds. 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 offset spatual. Return cake to refrigerator and chill until set, at least 2 1/2 hours.

To serve: If using, garnish top of cake with chocolate curls or dust with cocoa. Run thin knife between cake and side of springform pan; remove side of pan. Run cleaned knife along outside of cake to smooth sides. Cut into slices and serve.