Beat the butter until smooth, gradually stir in the sugar. Stir in eggs one by one, stir in rum flavor and sour cream. Mix flour with baking powder, sieve onto the mixture and stir in.
Put half of the dough in a greased box, Gugelhupf or wreath pan, mix the other half with the Nutella and also place in the pan, using a fork to create a marble pattern.
Bake in a preheated oven at 175 ° C for approx. 1 hour. Make a chopstick test.
Tip: sour cream or crème fraîche can be substituted for sour cream. Use 2 - 4 tablespoons of rum instead of flavors. Depending on your taste, vary between 2 teaspoons and 4 tablespoon nut nougat cream.