For the chocolate muffins, melt the butter with the chocolate in a bain-marie and leave to cool slightly. Separate the eggs, beat the egg whites until very stiff.
Cream the egg yolks with the sugar, then stir in the chocolate-butter mixture. Mix in the hazelnuts and divide the batter among 12 muffin cups.
Bake at 150 degrees convection for 25 minutes.
For the topping, cream the butter, powdered sugar, vanilla sugar, milk and rum flavoring and pipe onto the cooled muffins with a piping bag.
For the doctor hat, color the marzipan black and shape accordingly. Put it on the chocolate muffins and you’re done.