Preheat the oven to 350 degrees. Grease and flour a half sheet pan and set aside.

In a medium sized mixing bowl, combine the cake mix, water, milk, oil and eggs. Beat on medium speed for 2-3 minutes. Pour the cake batter into the prepared sheet pan and spread evenly over the sheet pan. Lightly tap the bottom of the sheet pan on the counter to remove any air bubbles.  Bake for 15 minutes or until the cake is golden brown on top and lightly springs back when touched. Remove to a wire rack. 

While the cake is baking, combine 1 1/2 cups hot coffee and 1 1/2 Tablespoons sugar, stirring until the sugar has dissolved. After removing from the oven while the cake is still hot, use a large fork or skewer and poke holes all throughout the surface of the cake. Then pour the hot coffee syrup over the cake, letting the coffee soak into the cake through the holes. Allow the cake to cool to room temperature. 

In another mixing bowl, beat together the mascarpone, cream cheese, sour cream, powdered sugar and vanilla extract. Fold in the whipped topping. Spread the cheese frosting evenly over the cooled cake. Sift unsweetened cocoa over the top of the cake and sprinkle with chocolate curls. Refrigerate until time to serve.