For the dough, mix the flour, baking powder, sugar and vanilla sugar together. Add eggs, butter and milk and mix into a batter. Cut the marzipan into very small pieces and fold in.
Grease and flour the muffin pan. Pour in the dough, press 2-3 washed and stemmed grapes into the dough. Bake in a preheated oven at around 180 degrees for 20-25 minutes. Let the muffins cool and dust with powdered sugar.