Beat the softened butter and sugar until frothy. Gradually stir in the eggs. Add baking powder, flour, salt and milk and work everything into a smooth dough.
Halve the dough and mix the Nutella under one half. First pour the light-colored dough into the mold, then the dark one. Make a spiral pattern with a fork. Bake in a preheated oven (150 ° C fan oven or 175 ° C top / bottom heat) for approx. 60 minutes. Depending on the oven and baking pan, you also need a higher temperature and possibly a longer baking time. In any case, test with the stick sample!
The amount is enough for a 26 cm springform pan with tube bottom. If you like, the cake can be coated with powdered sugar or chocolate icing.