Rum-Mocha Walnut Layer Cake
Active: 1 hour 30 minutes
Total: 3 hours
- Fine dry bread crumbs, for dusting
- 2 cups walnut halves (about 7 ounces)
- 1/4 cup unsweetened cocoa powder (not Dutch process)
- 1/2 cup cake flour
- 1 teaspoon instant espresso powder
- 8 large egg, separated
- 1 cup sugar
- 2 teaspoons pure vanilla extract
- 1/4 teaspoon salt
- 6 large egg yolks
- 1/2 cup sugar
- Pinch of salt
- 2 tablespoons instant espresso powder dissolved in 1/2 cup water
- 1 pound unsalted butter, softened
- 3 tablespoons coffee liqueur
- 1 tablespoon pure vanilla extract
- 1/4 cup dark rum, for brushing
- 1 1/2 cups finely chopped walnuts (about 5 ounces), plus walnut halves for garnish
- MAKE AHEAD: The cake can be refrigerated for up to 4 days.
1.MAKE THE CAKE: Preheat the oven to 350 degrees. Butter two 9-inch round cake pans and line the bottoms with parchment paper. Butter the parchment and dust with breadcrumbs, tapping out any excess. In a food processor, pulse the walnuts until finely chopped. Add the cocoa powder, cake flour and espresso powder and pulse until the walnuts are finely ground, Transfer to a bowl.
2.In a large bowl, using an electric mixer, beat the yolks at medium speed until thick and pale, 3 minutes. Beat in 2/3 cup of the sugar;increase the speed to high and beat until thick, about 5 minutes. Beat in the vanilla. In a medium bowl, using clean bearers, beat the egg whites and salt at medium speed until soft peaks form. Gradually add the remaining 1/2 cup of sugar and beat at high speed until the whites are stiff and glossy. Fold the egg whites and ground walnuts into the yolk mixture in 3 batches; fold just until no streaks remain.
3.Divide the batter between the prepared pans; smooth the tops. Bake for about 20 minutes, until the cakes are golden and springy. Transfer to a rack for 10 minutes, then invert the cakes and cool completely. Peel off the parchment; turn the cakes right side up.
4.MAKE THE FILLING: Fill a medium bowl with ice water. In a medium heat-proof bowl, whisk the yolks, sugar, and salt. Gradually whisk in the dissolved espresso. Place the bowl over a saucepan of barley simmering water and cook, stirring with a spatula, until the yolks are thick enough to coat the spatula and an instant-read thermometer inserted into the mixture registers 375 degrees, about 10 minutes. Set the bowl in the ice bath and cool, stirring occasionally.
5.In a large bowl, using an electric mixer, beat the butter at medium speed until smooth. Beat in the yolk mixture in 4 batches, beating well between additions. Beat in the liqueur and vanilla.
6.Using a serrated knife, split each cake in half horizontally. Set a top layer, cut side up, on a cake plate;brush it with 2 tablespoons of the rum and spread with 1/2 cup of the filling. Top with a bottom layer cake;brush with 2 more tablespoons of the rum and spread with another 1/2 cup of filling. Repeat with the remaining top cake layer, ending with the bottom layer, cut side down. Brush the top of the cake with the remaining 2 tablespoons of rum and spread the sides of the cake with a thin layer of filling. Spread the remaining filling on the top. Press the chopped walnuts around the side of the cake. Refrigerate the cake for at least 4 hours or overnight. Let the cake stand at room temperature for 15 minutes, then scatter the walnut halves on top before serving.