If using, prepare Chocolate Sponge Cake. Cut cooled cake in half crosswise. Line a 2-quart baking dish with one of the cake portions, cutting to fit as necessary. (Or layer half of the ladyfingers in a 2-quart baking dish, cutting to fit as necessary.) Drizzle with 2 tablespoons of the espresso and, if desired, 1 tablespoon of the liqueur.
In a small microwave-safe bowl microwave 3 ounces chopped chocolate on 50 percent power (medium) about 1 minute or until melted and smooth, stirring after every 15 seconds; cool.
In a large mixing bowl beat mascarpone cheese, whipping cream, powdered sugar, and vanilla with an electric mixer on medium speed until soft peaks form (tips curl). Beat in 2 tablespoons liqueur and cooled chocolate just until combined.
Spoon half of the mascarpone mixture over cake or ladyfingers in baking dish, spreading evenly. Top with the remaining cake portion or ladyfingers, cutting to fit as necessary. Drizzle with the remaining 2 tablespoons espresso and, if desired, the remaining 1 tablespoon liqueur. Top with the remaining mascarpone mixture, spreading evenly.
Cover and chill for 6 to 24 hours. If desired, garnish with melted chocolate and coffee beans.
Chocolate Sponge Cake
Allow eggs to stand at room temperature for 30 minutes. Meanwhile, grease a 15x10x1-inch baking pan. Line bottom of pan with parchment or waxed paper. Grease and flour paper and sides of pan; set pan aside. In a small bowl stir together flour, cocoa powder, baking powder, and salt; set aside.
Preheat oven to 350 degrees F. In a medium mixing bowl beat eggs with an electric mixer on high speed about 4 minutes or until thick and lemon-color. Gradually add granulated sugar, beating on medium speed for 4 to 5 minutes or until light and fluffy. Add flour mixture; beat on low to medium speed just until combined. In a small saucepan heat and stir milk and butter until butter is melted. Add butter mixture and vanilla to egg mixture, beating until combined. Pour batter into the prepared baking pan, spreading evenly.
Bake for 15 to 20 minutes or until a wooden toothpick inserted near the center comes out clean. Cool in pan on a wire rack for 10 minutes. Immediately loosen sides of cake from pan and turn cake out onto a clean kitchen towel sprinkled with powdered sugar. Carefully remove paper. Cool cake completely.