Using a serrated knife, cut the angel food cake horizontally into 4 equal layers. In a blender, process the cottage cheese until smooth. In a bowl, combine the coffee and 3 tbsp liqueur, if desired. In another bowl, whisk the remaining 2 tbsp liqueur with the cottage cheese, mascarpone, skim milk and sugar. In a shallow 8 x 8 inch baking dish, arrange 2 of the layers of cake, tearing it into pieces so that it covers the bottom of the dish. Sprinkle half of the coffee mixture evenly over the cake and top with half the cheese mixture, spreading it evenly. Arrange the remaining 2 layers of cake on top of the mascarpone, tearing it into pieces so that it covers the cheese. Sprinkle with the remaining coffee mixture and then top with the remaining cheese. Using a vegetable peeler, grate the chocolate over the top of the cake. Cover loosely with aluminum foil and refrigerate at least 24 hours. Bring to room temperature before serving.