Preheat oven to 350 degrees. Grease and flour 3 (9-in) pans.
Prepare cake mix according to package directions. Divide two-thirds of batter between 2 pans. Stir instant coffee into remaining batter; pour into remaining pan.
Bake in preheated oven for 20 to 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. In a measuring cup, combine brewed coffee and 1 Tablespoon coffee liqueur; set aside.
To make filling: In a small bowl, using an electric mixer set on low speed, combine mascarpone, 1/2 cup confectioners' sugar and 2 Tablespoons coffee liqueur; beat just until smooth. Cover with plastic wrap and refrigerate.
To make frosting: In a medium bowl, using an electric mixer set on medium-high speed, beat the cream, 1/4 cup confectioners' sugar and 2 Tablespoons coffee liqueur until stiff. Fold 1/2 cup of cream mixture into filling mixture.
To assemble the cake: Place one plain cake layer on a serving plate. Using a thin skewer, poke holes in cake, about 1 inch apart. Pour one-third of reserved coffee mixure over cake, then spread with half of the filling mixture. Top with coffee-flavored cake layer; poke holes in cake. Pour another third of the coffee over the the second layer and spread with the remaining filling.
Top with the remaining cake layer; poke holes in cake. Pour remaining coffee mixture on top. Spread sides and top of cake with frosting. Place cocoa in a sieve and lightly dust top of cake. Garnish with chocolate curls. Refigerate 30 minutes before serving
NOTE: To make curls, use vegetable peeler and run it down edge of chocolate bar.