Muffin with egg liqueur in choco cup

For 12 muffins: 

80 g melted butter

0.5 cup sugar

2 eggs

1 Tbsp vanilla sugar

1.5 cup of flour

1 tsp baking powder

pinch of salt

0.5 cup sour cream

For the filling:

150 ml egg liqueur

2 Tbsp vanilla custard-powder

200 ml milk

12 choco cups

Stir the custard-powder with the milk and boil the mix then add the liqueur to this pudding, let it get cold.
Fill the choco cups with the liqueur-pudding.
Preheat oven to 180°C
Mix butter with eggs, sugar and vanilla sugar in a bowl. Mix flour, salt and baking powder in an other bowl and then a half of this dry-ingredient-mix needs to be added to the wet mix (egg-butter-sugar) and stir them. Add the sour cream and the second part of the flour-mix to the dough and stir them roundly.
Dose the mix into a muffin form (for 12 pieces) put the filled choco cups into their center, cover the cups with dough and bake them around 12-15 minutes long in preheated oven (180°C)
Be careful with the hot muffins! Let them get colder before serving