Grease the fat pan (approx. 32 x 39 cm) and dust with flour. Melt 200 g butter, let it cool down a little. Coarsely chop the chocolate and nuts separately. Mix 150 g flour, sugar, cocoa, baking powder, vanillin sugar and 1 pinch of salt.
Beat the eggs in a large mixing bowl with the whisk of the hand mixer until creamy. Allow butter to run in, stir in. Stir in the flour mixture in several portions individually. Stir in crème fraiche.
Fold in chocolate and nuts.
Smooth the dough in the fat pan. Bake in the preheated oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer) for 25-30 minutes. Remove and let cool off. Dust with icing sugar and cut into pieces.
Sweetened strawberries, possibly with whipped cream, taste good with it.