Preheat oven to 350°F. Grease and flour three 9-inch round pans.

Prepare the white cake mix according to package directions.

Divide two-thirds of the batter between two pans.

Stir instant coffee powder into the remaining batter and pour into the remaining pan.

Bake in the preheated oven for 20-25 minutes, or until a toothpick inserted into the center comes out clean.

Let cool in pan for 10 minutes, then turn out onto a wire rack and cool completely.

Combine brewed coffee and 3 tablespoons Kahlua in a measuring cup; set aside for soaking the cake layers.

In a small bowl, combine mascarpone cheese, 1/2 cup powdered sugar, and 2 tablespoons Kahlua using an electric mixer on low speed. Beat until smooth.

Cover the mascarpone filling with plastic wrap and refrigerate to chill.

In a medium bowl, beat heavy cream, 1/4 cup confectioners' sugar, and 2 tablespoons Kahlua with an electric mixer on medium-high speed until stiff peaks form for frosting.

Fold 1/2 cup of the whipped cream frosting into the mascarpone filling.

Place one plain cake layer on a serving plate.

Using a thin skewer, poke holes in the cake layer, about 1 inch apart.

Spoon one-third of the coffee-Kahlua mixture over the cake layer, then spread with half of the mascarpone filling mixture.

Top with the coffee-flavored cake layer; poke holes in the cake.

Spoon another third of the coffee-Kahlua mixture over the coffee-flavored layer and spread with the remaining filling.

Top with the remaining plain cake layer; poke holes in the cake.

Spoon the remaining coffee-Kahlua mixture on top of the cake.

Spread the sides and top of the cake with the Kahlua-flavored whipped cream frosting.

Place cocoa powder in a sieve and lightly dust the top of the cake with cocoa.

Garnish the cake with chocolate curls.

Refrigerate the assembled cake for at least 30 minutes before serving.

To make the chocolate curls, use a vegetable peeler and run it down the edge of the semisweet chocolate square.