Grease a ring cake tin (2.5 l capacity) and dust with flour. Roughly chop the chocolate. Preheat the oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer).
Cream 250 g butter, sugar, vanilla sugar and 1 pinch of salt with the whisks of the mixer. Stir in the eggs one by one. Mix 250 g flour and baking powder and stir in alternately with the egg liqueur.
Fold in the chopped chocolate.
Fill the dough into the mould and smooth it down. Bake in a hot oven for 55-60 minutes. Remove from the oven and leave to cool in the mould for about 30 minutes. Then turn out of the tin and let it cool down. Dust with icing sugar.