Triple-Chocolate Mousse Cake
Bottom Layer
6 tablespoons unsalted butter, cut into 6 pieces
7 ounces bittersweet chocolate, chopped fine
¾ teaspoon instant espresso powder
4 large eggs, separated
1½ teaspoons vanilla extract
Pinch cream of tartar
Pinch salt
1/3 cup packed (2 1/3 ounces) light brown sugar
Middle Layer
5 tablespoons hot water
2 tablespoons Dutch-processed cocoa powder
7 ounces bittersweet chocolate, chopped fine
1½ cups heavy cream, chilled
1 tablespoon granulated sugar
1/8 teaspoon salt
Top Layer
¾ teaspoon unflavored gelatin
1 tablespoon water
1 cup (6 ounces) white chocolate chips
1½ cups heavy cream, chilled
Shaved chocolate (optional)
For the Bottom Layer
Adjust oven rack to middle position and heat oven to 325 degrees Fahrenheit. Grease 9½-inch springform pan. Melt butter, chocolate, and espresso powder in a large heatproof bowl set over a saucepan filled with 1 inch barely simmering water, stirring occasionally, until smooth. Remove from heat and let cool slightly, about 5 minutes. Whisk in egg yolks and vanilla; set aside.
Using stand mixer fitted with whisk, whip egg whites, cream of tartar, and salt on medium-low speed until foamy, about 1 minute. Add half of sugar and whip until combined, about 15 seconds. Add remaining sugar, increase speed to high, and whip until soft peaks form, about I minute longer, scraping down bowl halfway through whipping. Using hand whisk, fold one third 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 pan and smooth top with rubber spatula.
Bake cake until risen, firm around edges, and center springs back after you press gently with your finger, 13 to 18 minutes, rotating pan halfway through baking. Transfer cake to wire rack and let cool completely, about 1 hour, before filling. (Cake will collapse as it cools.) Do not remove cake from pan.
For the Middle Layer
Combine hot water and cocoa in small bowl; set aside. Melt chocolate in large heatproof bowl set over saucepan filled with 1 inch barely simmering water, stirring occasionally, until smooth. Remove from heat and let cool slightly, 2 to 5 minutes.
Using stand mixer fitted with whisk, whip cream, sugar, and salt on medium-low speed until foamy, about 1 minute. Increase speed to high and whip until soft peaks form, 1 to 3 minutes.
Whisk cocoa mixture into melted chocolate until smooth. Using hand 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 pan over cooled cake, smooth top with offset spatula, and gently tap pan on counter to release air bubbles. Wipe inside edge of pan with damp cloth to remove any drips. Refrigerate cake for at least 15 minutes.
For the Top Layer
Sprinkle gelatin over water in small bowl and let sit until gelatin softens, about 5 minutes. Place chocolate chips in medium heatproof 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 chocolate chips and let sit, covered, for 5 minutes. Whisk mixture gently until smooth. Let cool completely. Stirring occasionally (mixture will thicken slightly).
Using stand mixer with fitted whisk, whip remaining 1 cup cream on medium-low speed until foamy, about 1 minute. Increase speed to high and whip until soft peaks form, 1 to 3 minutes. Using hand whisk, fold one-third of whipped cream into white chocolate mixture to lighten. Using rubber spatula, fold in remaining whipped cream until no white streaks remain. Spoon white chocolate mousse into pan over middle layer and smooth top with offset spatula. Return cake to refrigerator and chill until set, at least 2½ hours. Assembled cake can be refrigerated for up to 24 hours.
Garnish top of the cake with shaved chocolate, if using. Run thin knife between cake and sides of pan; remove sides of pan. Run cleaned knife along side of the cake to smooth. For clean slices, dip your knife into hot water before cutting each slice.
Notes: This recipe requires a springform pan that is at least 3 inches high. Be sure to let the bottom layer cool completely before topping it with the middle layer.
Recipe from Cook’s Illustrated.
Bon Appétit,
professorca 