“Thin, delicate layers of flourless chocolate cake are filled with silky chocolate-espresso mousse. Begin making this dessert at least one day ahead, and serve it straight from the freezer; the frozen mousse filling has the texture of soft ice cream.”
4ouncesbittersweetnot unsweetened or semisweet chocolate, chopped
5large egg yolks
¼cupsKahlúa or other coffee liqueur
1cupchilled heavy whipping cream
2 ½teaspooninstant espresso powder
½cupfinely chopped bittersweetnot unsweetened or semisweet chocolate
¼cupKahlúa or other coffee liqueur
1tablespoonlight corn syrup
6ouncesbittersweetnot unsweetened or semisweet chocolate, chopped
2tablespoonswhole coffee beans
FOR THE CAKE
Position rack in center of oven and preheat to 375° F.
Lightly butter two 9-inch-diameter cake pans with 1 ½-inch-high sides. Line the bottom of the pans with parchment paper. Set aside.
Combine chocolate and water in top of double boiler set over simmering water. Stir until chocolate is smooth. Remove from over water. Transfer chocolate to large bowl; cool 5 minutes. Whisk egg yolks into chocolate.
Beat whites in medium bowl until soft peaks form. Add sugar 1 tablespoon at a time, beating until stiff and glossy. Fold ¼ of egg whites into chocolate to lighten. Gently fold remaining egg whites into chocolate mixture in 2 additions, just until combined, being careful not to deflate batter.
Divide batter between prepared pans (layers will be very thin). Bake until cakes begin to pull away from sides of pans and wooden cake tester or toothpick inserted into center comes out clean, about 10 minutes. Cool cakes in pans on wire rack for 1 hour.
Once cooled, carefully invert cakes onto 9-inch-diameter cardboard rounds or tart pan bottoms. Cool cakes completely. Peel off parchment paper.
FOR THE FILLING
While waiting for the cakes to cool, line 9-inch-diameter cake pan with 1 ½-inch-high sides (we reused one that we previously baked in) with plastic wrap, leaving 5-inch overhang. Set aside.
Whisk egg yolks, ¼ cup of the sugar, and Kahlúa in medium metal bowl to blend. Set bowl over saucepan of simmering water (do not allow bottom of bowl to touch water). Using hand-held electric mixer, beat until yolk mixture is thick and instant-read thermometer inserted into mixture registers 140°F for 3 minutes, about 9 minutes total. Remove bowl from over water. Continue to beat mixture until cool to touch, about 3 minutes.
Beat whipping cream and espresso powder in another medium bowl until firm peaks form. Fold cream mixture into yolk mixture in 2 additions.
Using clean dry beaters, beat egg whites in large bowl until soft peaks form. Gradually add remaining ¼ cup sugar and beat until stiff and glossy. Gently fold egg white mixture into yolk mixture in 2 additions. Fold in chopped chocolate.
Carefully place one completely cooled cake layer in the bottom of the prepared pan (cake layer is very delicate).
Spread the filling evenly over first cake layer (filling layer will be thick). Top with second cake layer; press gently to adhere. Fold plastic overhang over cake, then cover with foil. Freeze cake overnight. DO AHEAD Can be made 3 days ahead. Keep frozen.
FOR THE GLAZE
Invert cake onto 9-inch-diameter cardboard round or tart pan bottom; place on rack set over rimmed baking sheet. Set aside.
Bring cream, Kahlúa, and corn syrup to a simmer in small saucepan. Remove from heat. Add chocolate; whisk until smooth. Transfer ½ cup glaze to small bowl; chill until cool and very slightly thickened but easily spreadable (if too thick, glaze will not spread smoothly on frozen cake), about 10 minutes
Meanwhile while you wait for the glaze to cool, remove foil and plastic wrap from top of cake. Working quickly, spread thin layer of chilled glaze over top and sides of cake. Freeze until glaze is set, about 1 hour.
Rewarm remaining glaze over low heat until just warm and pourable. Transfer to ½-cup measuring cup. Pour this ½-cup of glaze over top of cake. Using an offset spatula, quickly spread the glaze over top, allowing excess to run down sides of cake; smooth over sides (glaze will harden quickly on frozen cake). Pour remaining glaze over top of cake; spread quickly and smoothly over top and sides. Sprinkle coffee beans around top edge of cake. Freeze until firm and glaze is set, at least 4 hours. DO AHEAD Can be made 3 days ahead. Cover; keep frozen.