Step 1

Make the tortes: Heat oven to 350°F. Butter the bottoms of two 10-inch round cake pans and fit with two circles of parchment paper. Butter the paper and pan sides. Set aside. Combine the ground walnuts, flour, cornstarch, and baking powder and set aside. Place the egg whites and salt together in a large bowl, beat to stiff peaks, and set aside.

Step 2

Place the egg yolks in a large bowl and beat on medium-high speed. Gradually add the granulated sugar and continue to beat until the mixture becomes thick and fluffy, about 5 minutes. Add 2 teaspoons vanilla, mix to combine and set aside. Sprinkle the walnut mixture over the yolk mixture and fold in the egg whites until combined. Divide the batter between the prepared pans and bake until the cake centers spring back when lightly touched, 25 to 30 minutes. Run a knife around the pan sides and turn the cakes out onto wire racks. Cool completely.

Step 3

Make the mocha frosting and coffee filling: Beat the butter, chocolate, remaining 1 1/2 teaspoons vanilla, and 1 1/2 cups confectioners' sugar together until creamy. Alternately add the coffee, liqueur, and 4 1/2 more cups of confectioners' sugar and continue to beat until fluffy. Set aside. Beat the heavy cream, instant coffee, and remaining 1/4 cup confectioners' sugar to soft peaks.

Step 4

Assemble the cake: Split the tortes. Place one split layer on a cake plate and spread 3/4 cup mocha frosting over top. Follow with a third of the coffee cream. Place second layer on top and repeat with frosting and cream. Repeat with third layer. Place the final layer on the cake and spread the remaining mocha frosting over the top and sides of cake. Decorate with the chopped walnuts. Refrigerate until ready to serve.