Leschanz’s Chocolate Mousse Cake

Leschanztorte

Preparation info

  • Difficulty

    Medium

  • Makes

    12 to 16

    servings

Appears in

Wolfgang Leschanz, an extraordinary baker who has worked at both Sacher and Demel, spent an afternoon with me demonstrating his specialties. This two-tone chocolate cake is deceptively easy for all its richness. Look at the ingredients: both the filling and the cream topping are practically identical in ingredients and proportions, but they are manipulated to give amazingly different results. The first mixture is baked and cools into a thin, fudgy cake that falls in the center. It’s supposed to do that—all the better for spreading with the chocolate mousse filling.

Ingredients

Cake

  • ounces high-quality bittersweet chocolate, finely chopped
  • ¾ cup ( sticks) unsalted butter, at room temperature, cut into 12 pieces
  • 7 large eggs, separated, at room temperature
  • 1 cup plus 2 tablespoons sugar

Mousse Topping

  • ounces high-quality bittersweet chocolate, finely chopped
  • ¾ cup ( sticks) unsalted butter, at room temperature, cut into 12 pieces
  • cups confectioners’ sugar
  • 6 large eggs
  • About 2 ounces chocolate curls, for garnish

Method

  1. To make the cake: Position a rack in the center of the oven and heat to 350°F. Lightly butter the inside of a 9-inch springform pan. Dust with flour and tap out the excess.
  2. In a large metal bowl set over a pot of hot, not simmering, water, melt the chocolate. Remove from the heat. Whisk in the butter, one piece at a time. Whisk in the egg yolks.
  3. In a large bowl, using a handheld electric mixer on low speed, beat the egg whites until they form soft peaks. Gradually beat in the sugar and beat until they form stiff, shiny peaks. Stir one fourth of the beaten whites into the chocolate mixture, then fold in the remainder. Spread evenly in the pan.
  4. Bake until the top is puffed, cracked, and crisp, and a toothpick inserted in the center comes out clean, about 30 minutes. Remove from the oven and run a sharp knife around the inside of the pan to release the cake from the sides. Transfer to a wire rack and cool completely in the pan. Don’t worry if the cake sinks.
  5. To make the topping: Melt the chocolate in the top part of a double boiler over hot, not simmering, water, or in a microwave on medium power. Remove from the heat. Cool, stirring often, until the chocolate is tepid.
  6. In a large bowl, using a handheld electric mixer at low speed, beat the butter and confectioners’ sugar until combined. Increase the speed to high and beat until light and fluffy, about 2 minutes. Beat in the cooled chocolate. One at a time, beat in the eggs.
  7. Spread the topping evenly over the cake in the pan. Cover the pan tightly with plastic wrap. Refrigerate until the topping is set, at least 4 hours or overnight.
  8. To serve, rinse a thin sharp knife under hot water and run it inside the pan to release the cake. Remove the sides of the pan. Garnish the top of the cake with the chocolate curls. Using a thin, sharp knife rinsed under hot water, slice the cake. Serve chilled.

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