Beat butter or margarine with the hand mixer on the highest setting until smooth. Gradually stir in the sugar and vanilla sugar and stir until a bond has formed. Gradually stir in the eggs (each egg about 1/2 minute)
Mix the flour with baking powder, stir in portions alternately with the milk on a medium setting.
Cut the chocolate bar into slivers or fine cubes. Now stir the chopped chocolate into the batter.
Fill the dough up to a good 2/3 either in paper cases or in the muffin tin.
Bake the muffins at 180-200 ° C for about 15-20 minutes. Let the muffins cool and decorate with the powdered sugar and lemon juice mixture.