Put the oven on preheating to 180 C. Grease the prepared muffin pan with oil. (I have paper forms, I don't have them.
Melt the chocolate with butter (in a water bath or in a microwave oven)
Mix flour with baking powder.
Beat sugar, salt, eggs and vanilla sugar until creamy.
Carefully pour in the flour in several steps. Mix it.
Now add the melted chocolate. Spread the dough into muffin molds and bake for about 20 minutes.