Triple-Chocolate Mousse Cake

By MarieR

(To rate a perfect 10, this triple-decker would need to lighten up.)
Each layer possesses a unique texture and richness. "triple-chocolate mousse cake is a tower of dark, milk, and white chocolate. By finessing each layer, I aimed to build a triple-decker that was incrementally lighter in
texture — and richness — with each new tier.
Since the bottom layer would need to support two tiers, a flourless chocolate cake fit the bill. For the middle layer, I started with a basic dark chocolate mousse recipe. To distinguish it from the bottom layer, I reduced the amount of bittersweet chocolate, eliminated the eggs, and upped the whipped cream. My second tier was now light, chocolaty, and creamy.
Ideally, the crowning mousse layer would be ethereally silky, so I folded melted white chocolate into whipped cream and layered it on top of the dark chocolate mousse. The texture was light, but it oozed during slicing, so I added gelatin to firm it up. The only accessorizing this cake needed was a few wispy curls of chocolate.
Cook's Illustrated

Ingredients

• BASE LAYER:
• Triple-Chocolate Mousse Cake
• MAKES ONE 91/2 4-INCH CAKE, SERVING 12 TO 16
• NOTE: Ghirardelli Bittersweet Chocolate Baking Bar is the test kichen favorite. For neat layers, dip the knife into hot water before cutting each slice.
• 6 tablespoons (3/4 stick) unsalted butter,cut into 6 pieces
• 7 ounces bittersweet chocolate, chopped fine(see note)
• 3/4 teaspoon instant espresso powder (instant coffee powder will do)
• 1 1/2 teaspoons vanilla extract
• 4 large eggs, separated
• Pinch salt
• 1/3 cup packed (21/2 ounces) light brown sugar
• MIDDLE LAYER
• 2 tablespoons Dutch-processed cocoa powder
• 5 tablespoons hot water
• 7 ounces bittersweet chocolate, chopped fine
• 1 1/2 cups cold heavy cream
• 1 tablespoon sugar
• 1/8 teaspoon salt
• TOP LAYER
• 3/4 teaspoon powdered gelatin
• 1 tablespoon water
• 6 ounces white chocolate, chopped fine 1 1/2 cups cold heavy cream
• Shaved chocolate for serving (optional)

Details

Servings 16

Preparation

Step 1

1. FOR THE BASE LAYER: Adjust an oven rack to the middle position and heat the oven to 325 degrees. Grease the bottom and sides of a 91A by 3-inch springform pan. Melt the butter, chocolate, and espresso powder 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 the mixture slightly, about 5 minutes. Whisk in the vanilla and egg yolks; set aside.
2. 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 seconds. Add half of the brown sugar and beat until combined, about 15 seconds. Add the remaining brown sugar and beat at high speed until soft peaks form, about 1 minute longer, scraping down the sides halfway through. Using a whisk, fold one-third of the beaten whites into the chocolate mixture. Using a rubber spatula, fold in the remaining whites until no streaks remain. Transfer the batter to the springform pan, gently smoothing the top with a spatula.
3. Bake until the cake's center has set but is still soft (it will spring back after pressing gently with your finger), 13 to 18 minutes.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.
4. FOR THE MIDDLE LAYER: 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 minutes.
5. In the clean bowl of a stand mixer fitted with the whisk attachment, whip the cream, sugar, and salt at medium speed until it begins to thicken, about 30 seconds. Increase the speed to high and whip until soft peaks form, 15 to 60 seconds. Whisk the cocoa powder mixture into the melted chocolate until smooth. Using a whisk, fold one-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 springform pan with a damp cloth to remove any drips. Refrigerate the cake at least 15 minutes while preparing the white chocolate mousse.
6. FOR THE TOP LAYER: In a small bowl, sprinkle the gelatin over the water; let stand at least 5 minutes. Place the white chocolate in a medium bowl. Bring '/> cup of the cream to a simmer in a 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 seconds. Cool to room temperature, stirring occasionally, 5 to 8 minutes, until thickened.
7. In the clean bowl of a stand mixer fitted with the whisk attachment, whip the remaining 1 cup cream at medium speed until it begins to thicken, about 30 seconds. Increase the speed to high and whip until soft peaks form when the whisk is lifted, 15 to 60 seconds. Using a whisk, fold one-third of the whipped cream into the white chocolate mixture to lighten. Using a rubber spatula, fold 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 2/4 hours. (The cake can be refrigerated up to 1 day; let it sit at room temperature for 45 minutes before releasing from the cake pan and serving.)
8. TO SERVE THE CAKE: Garnish the top with chocolate curls (if using). Run a thin knife around the inside of the springform pan; remove the side of the pan. Smooth the side of the cake with a clean knife. Cut into slices and serve.