Triple Chocolate Mousse Cake

Triple Chocolate Mousse Cake

Adapted from America's Test Kitchens

Makes one 9-inch cake

Ingredients

Bottom Layer

• 6 tbsp (3/4 stick) unsalted butter, cut into 6 pieces, plus more for greasing pan
• 7 oz bittersweet chocolate, chopped finely
• 3/4 tsp instant espresso powder
• 1-1/2 tsp vanilla extract
• 4 large eggs, separated
• Pinch table salt
• 1/3 cup packed (about 2-1/2 oz) light brown sugar, crumbled with fingers to remove lumps

Middle Layer

• 2 tbsp cocoa powder, preferably Dutch-processed
• 5 tbsp hot water
• 7 oz bittersweet chocolate, chopped finely
• 1-1/2 cups cold heavy cream
• 1 tbsp granulated sugar
• 1/8 teaspoon table salt

Top Layer

• 3/4 tsp powdered gelatin
• 1 tbsp water
• 6 oz white chocolate chips or chopped white chocolate
• 1-1/2 cups cold heavy cream
• Shaved chocolate or cocoa powder for serving (optional)

• 1. FOR THE BOTTOM LAYER: Place oven rack to middle position and heat oven to 325 degrees F. Butter bottom and sides of 9-1/2-inch springform pan. Melt butter, chocolate, and espresso powder in a large heatproof bowl set over saucepan filled with 1 inch of barely simmering water (double boiler), stirring occasionally until smooth. Remove from heat and cool mixture slightly, about 5 min. Whisk in vanilla and egg yolks and set aside.
• 2. In stand mixer fitted with whisk attachment, beat egg whites and salt at medium speed until frothy, about 30 sec. Add half of the brown sugar and beat until combined, about 15 sec. Add remaining brown sugar and beat at high speed until soft peaks form when whisk is lifted, about 1 min. longer, scraping down sides halfway through. Using whisk, fold 1/3 of 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 springform pan, gently smoothing top with offset spatula.
• 3. Bake until cake has risen, is firm around edges, and center has just set but is still soft (center of cake will spring back after pressing gently with finger), between 13 to 18 minutes. Transfer cake to wire rack to cool completely for about 1 hour. (Cake will collapse as it cools.) Do not remove cake from pan.
• 4. FOR THE MIDDLE LAYER: Combine cocoa powder and hot water in small bowl and set aside. Melt chocolate in large heatproof bowl set over saucepan filled with 1 inch of barely simmering water (double boiler), stirring occasionally until smooth. Remove from heat and cool slightly, 2 to 5 min.
• 5. In a clean bowl of stand mixer fitted with the whisk attachment, whip cream, granulated sugar, and salt at medium speed until mixture begins to thicken, about 30 sec. Increase speed to high and whip until soft peaks form when whisk is lifted, 15 to 60 seconds.
• 6. Whisk cocoa powder mixture into melted chocolate until smooth. Using whisk, fold 1/3 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.
• 7. FOR THE TOP LAYER: In small bowl, sprinkle gelatin over water; let stand at least 5 min. Place white chocolate in medium bowl. Bring ½ 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 to 8 minutes (mixture will thicken slightly).
• 8. In a clean bowl of stand mixer fitted with the whisk attachment, whip remaining cup cream at medium speed until it begins to thicken, about 30 sec. Increase speed to high and whip until soft peaks form when whisk is lifted, 15 to 60 sec. Using whisk, fold 1/3 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 spatula. Return cake to refrigerator and chill until set, at least 2½ hours (best chilled overnight)
• 9. TO SERVE: If using, garnish top of cake with chocolate curls or dust with cocoa. Run thin knife between cake and side of spring form pan; remove side of pan. Run cleaned knife along outside of cake to smooth sides. Cut into slices and serve.