Place the chocolate in the freezer until it is hard, then grate. Whisk the butter, sugar, vanilla sugar, salt and eggs together well. Mix cocoa, flour and baking powder and sieve onto the butter mixture. Stir in with the Baileys. Then add the ground hazelnuts and the grated chocolate to the batter.
If the dough is too firm, add a little more water (swiveled in the slope of the Bailey in the measuring cup).
Pour the batter into a large cup cake pan. Bake at 150 degrees air circulation for about 70 to 90 minutes (toothpick test).
Brush the cooled cake with the dissolved cake icing.