Prepare a batter out of butter, sour cream, yolk, salt, flour and baking powder. Let rest in a cool place for 30 minutes.
Fullness:
Mix the nuts, sugar, vanilla sugar, egg white, rum and milk together.
Halve the dough. Roll out each half thinly into a circle and cut into 8 parts (like pieces of cake). Pour the filling on top, shape into croissants and bake at 180 degrees for 25 minutes.
Roll it in the vanilla sugar and icing sugar while it is still hot.