Preheat the oven to 220 degrees Celsius (428 degrees Fahrenheit). Grate the marzipan coarsely and lightly beat the egg whites. Put marzipan, egg whites, and powdered sugar in a bowl, mix briefly with a hand mixer. Knead to a firm, but soft and slightly sticky dough on a powdered sugar-dusted board. Press the dough flat, cut it into 4 or 8 pieces, depending on how large you want your marzipan cakes. Place a bar of nougat on each piece and fold the marzipan around it. Shape your pieces as desired and bake them for about 10 minutes - until they are nicely light brown. Let them cool, melt the chocolate, dip the pieces in the chocolate, cool again until the chocolate has hardened. Whisk egg white and powdered sugar together for icing and decorate your cakes with the icing. Sprinkle with chopped hazelnuts.