6 tbsp Unsalted Butter, cut into 6 pieces
7 oz. Bittersweet Chocolate, chopped fine
3/4 tsp. instant espresso powder
1 1/2 tsp. vanilla extract
4 lg. eggs, separated
1 pinch salt
1/3 cup packed light brown sugar
2 tbsp. Dutch-processed cocoa powder
5 tbsp. hot water
7 oz. bittersweet chocolate, chopped fine
1 1/2 cup cold heavy cream
1 tbsp sugar
1/8 tsp. salt
3/4 tsp powdered gelatin
1 tbsp. water
6 oz. white chocolate, chopped fine
1 1/2 cups cold heavy cream
Shaved Chocolate for serving (optional)
Adjust an oven rack to the middle position and heat the oven to 325 F. Grease the bottom and sides of a 9 1/2 by 3 inch spring form pan. Melt the butter, chocolate and espresso powder in a large heat proof bowl set over a saucepan filled with 1 inch of barely simmering water stirring occasionally until smooth. Remove from the heat and cool for 5 minutes. Whisk in the vanilla and egg yolks; set aside.
In the clean bowl of a stand mixer fitted with the whisk attachment, beat the egg whites and salt at medium speed until frothy, about 30 secs. Add half of the brown sugar and beat until combined, about 15 secs. Add the remaining brown sugar and beat at high speed until soft peaks form, about 1 minute longer,. Using a whisk, fold in one-third of the beaten whites into the chocolate mixture. Using a rubber spatula, ford in the remaining whites until no streaks remain. Transfer the batter to the spring form pan, gently smoothing the top with a spatula.
Bake until the cake's center has set but is still soft (it will spring back after pressing gently with your finger) 13-18 mins. Transfer the cake to a wire rack to cool completely, about 1 hour. The cake will collapse as it cools, do not remove the cake from the pan.
Combine the cocoa powder and hot water in a small bowl;set aside. Melt the chocolate in a large heatproof bowl set over a saucepan filled with 1 inch of barely simmering water, stirring occasionally until smooth. Remove from the heat and cool slightly. 2 to 5 mins.
In the clean bowl of a stanad mixer fitted with the whisk attachment, whip the cream, sugar and salt at the medium speed until it begins to thicken, about 30 secs. Increase the speed to high and whip until soft peaks form, 15 to 60 secs. Whisk in the cocoa powder mixture in the melted chocolate until smooth. Using a whisk, fold on-third of the whipped cream into the chocolate mixture. Using a rubber spatula, fold in the remaining whipped cream until no streaks remain. Spoon the mousse over the cooled cake and gently tap the pan on the counter 3 times to remove any large air bubbles: gently smooth the top with an offset spatula. Wipe the inside edge of the spring form pan with a damp cloth to remove any drips. Refrigerate the cake at least 15 mins while preparing the white chocolate mousse.
In a small bowl, sprinkle the gelatin over the water; let stand at least 5 mins. Place the white chocolate in a medium bowl. Bring 1/2 cup of the cream to a simmer in the small saucepan over medium-high heat. Remove from the heat; add the gelatin mixture and stir until fully dissolved. Pour the cream mixture over the chocolate and whisk until the chocolate is melted and the mixture is smooth, about 30 secs. Cool to room temperature, stirring occasionally, 5-8 mins, until thickened.
In the clean bowl of the stand mixer fitted with the whisk attachment, whip the remaining 1 cup cream at medium speed until it begins to thicken, about 30 secs. Increase the speed to high and whip until soft peaks form when the whisk is lifted, 15 to 60 secs. Using a whisk, fold in 1/3 of the whipped cream into the white chocolate mixture to lighten. Using a rubber spatula, fold in the remaining whipped cream into the white chocolate mixture until no white streaks remain. Spoon the white chocolate mousse into the pan over the bittersweet chocolate mousse layer. Smooth the top with an offset spatula. Return the cake to the refrigerator and chill until set, at least 2 1/2 hours. (The cake can be refrigerated up to 1 day; let it sit at room temperature for 45 mins before releasing the cake from the pan and serving)
Garnish the top with chocolate curls. Run a thin knife arougn teh inside of the springform pan;remove the side of the pan. Smooth the side of the the cake witha clean knife. Cut into slices and serve.
Recipe courtesy of America's Test Kitchen