Mix the semolina with the milk and let it soak for 10 minutes. In the meantime, mix the baking powder with the hazelnuts and cocoa powder.
In another bowl, beat the eggs, margarine, vanilla sugar and sugar until frothy. Fold in the swollen semolina and slowly add the hazelnut-cocoa mixture. Mix everything into a dough and pour into a greased 26-inch dish.
Put in the preheated oven and bake for about 30 minutes on the middle rack.