Finely grate the chocolate. Beat the egg whites until stiff and set aside. In another bowl, cream the butter until smooth. Gradually add sugar and vanilla sugar. Stir until a combined mass is formed.
Stir in cinnamon and rum flavoring. Gradually stir in egg yolks. Mix flour with baking powder and stir in briefly on medium speed. Stir in hazelnuts and rolled oats. Then fold in beaten egg whites and chocolate. Pour the batter into a springform pan (28 cm, bottom greased). For the topping, drain the cherries in a sieve. Spread the cherries and sliced hazelnuts on the dough. Bake the cake in a preheated oven at 180°C for about 50 minutes. Then remove from the pan and let cool. Dust with a little powdered sugar.