Mix butter, sugar, vanilla sugar and a pinch of salt until foamy. Add eggs one after the other and stir well. Mix baking powder with flour and stir in alternately with milk. The dough should be pliable and still come off the spoon. Then mix in the marzipan.
Fill the dough into the muffin pan and cover with the plum halves (max. 1 whole per muffin, otherwise the dough will be too mushy - depending on the type) and brush with a little dough so that everything is covered. Bake in the preheated oven at 200 degrees top / bottom heat for about 20-25 minutes.