Beat eggs, sugar and vanilla sugar until frothy. Add egg liqueur and oil. Mix flour with baking powder and sieve in. Pour half of the batter into a greased cup cake pan. Stir 2 tablespoons of cocoa and 100 g of grated chocolate into the remaining batter. Put the dark on the light dough and fold in a spiral with a fork. Bake in the oven at 175 degrees (convection) for approx. 60 minutes. Dust with icing sugar after baking.