Mix the butter, sugar and vanilla sugar until frothy. Gradually add the eggs and stir in thoroughly. Stir in the butter vanilla flavor and the milk. Mix the flour and baking powder and stir into the batter. Now stir in the mineral water until it is a nice, creamy batter.
Sometimes you need a little more and sometimes a little less mineral water. At the end, the grated chocolate goes into the batter. Then fill this dough into a box cake tin (30cm) lined with baking paper and bake at 180 ° C for about 50 - 60 minutes.
After cooling, heat the dark chocolate in a water bath and stir in the cream.