Ingredients Cake: 1 (15.25 ounce) package moist white cake mix 1 cup water 3 large egg whites ⅓ cup vegetable oil 1 teaspoon instant coffee powder
Filling: 1 (8 ounce) container mascarpone cheese ½ cup confectioners' sugar 2 tablespoons coffee flavored liqueur
Frosting: 2 cups heavy cream ¼ cup confectioners' sugar 2 tablespoons coffee flavored liqueur
Make the cake: Mix cake mix, water, egg whites, and oil in a large bowl with an electric mixer on medium speed for 2 minutes. Two prepared pans receive 2/3 of the batter. Mix instant coffee into remaining batter and pour into remaining pan.
Bake cakes for 23–28 minutes in the preheated oven until a toothpick inserted into the center comes out clean. Cool cakes in pans for 10 minutes, then transfer to wire rack to finish cooling.
Filling: Beat mascarpone, confectioners' sugar, and coffee liqueur in a medium bowl with a low-speed electric mixer until smooth. Keep cool in the fridge with plastic wrap.
The frosting: Beat cream, confectioners' sugar, and coffee liqueur in a medium bowl with an electric mixer on medium-high speed until firm. Combine 1/2 cup frosting with cold filling. Keep frosting and filling cool in the fridge covered.
Cake assembly: Serve 1 basic cake layer on a platter. Pierce cake 1 inch apart with a thin skewer. Cover cake with 1/3 coffee syrup and 1/2 filling.
Cover with coffee-flavored cake and poke holes. Pour 1/3 more coffee syrup over cake and top with remaining filling. Add last cake layer and poke holes. Pour leftover coffee syrup on top. Frost cake sides and top.
To garnish, lightly dust cake with cocoa powder from a sieve. Use a vegetable peeler to curl chocolate squares. Sprinkle chocolate curls on cake.