Roughly chop the chocolate and melt it over a warm water bath. Whip the fat, sugar, salt and vanilla sugar until creamy with the whisk of the hand mixer. Stir in the eggs one after the other. Mix flour and baking powder and stir in alternately with the milk. Remove a good 1/3 of the dough and stir in the grated coconut. Stir the melted chocolate and cocoa into the remaining dough. Grease the fat pan of the oven (32 x 39 cm).
Put half of the chocolate dough into a greased fat pan and smooth it down. Using a tablespoon, spread the coconut dough evenly in small heaps (so that gaps remain) on the dark dough. Pour the rest of the dark dough on top, carefully smooth it down so that the dark dough is finished. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 25 minutes. Remove from the oven, place on a rack and allow to cool. Dust lightly with icing sugar