Chop chocolate and nuts separately. Melt 100 g chocolate and butter over a warm water bath. Whisk the eggs with a whisk. Mix flour and baking powder in a bowl. Add sugar, vanilla sugar, salt, eggs and chocolate mixture, stir in nuts. Mix everything briefly with the whisk of the hand mixer to a smooth dough. Fold in the rest of the chopped chocolate
Line a square baking or casserole dish (16 x 16 cm) with baking paper. Pour in the dough and smooth it down. Bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for 25-30 minutes
Take out the cake, remove the baking paper. Let the cake cool down on a cake rack. Cut cake into pieces, arrange on a plate, decorate with raspberries and mint