Combine the dry ingredients (flour, cacao powder, baking powder and salt) in a bowl.
Melt the butter and dark chocolate au-bain marie.
Beat the eggs together with the sugar and vanilla sugar. Pour in the melted butter and mix well.
Add the dry mixture bit by bit. Cover the dough and put the bowl in the fridge for at least 2 hours.
Pre-heat the oven on 180 degrees. Form the dough into small balls and place them on a plate. Pour some confectioners sugar in a small bowl and roll the balls through this.Place them on a baking tray covered with parchment paper and bake for 12 minutes.