Mix the butter, eggs, sugar and vanilla sugar together. Stir in the cream. Chop the chocolate (not too small!) And fold into the batter. Mix in the flour, cocoa and baking powder.
Place paper liners in the muffin tin. Pour the dough into the molds in equal portions. Bake at 180 degrees for 20 minutes on the middle rack.
Before taking the muffins out of the mold, wait 5 minutes if possible. The muffins taste best fresh.