Preheat the oven to 180 ° C and line or grease the muffin tin with paper liners. Heat the milk and melt the Nutella in it and let it cool down. Mix the flour, nuts, cocoa and baking powder carefully.
Beat the egg with the sugar until frothy. Add the oil and Nutella milk and stir. Add the flour mixture and stir until the dry ingredients are moist (stirring too long makes the dough tough and the muffins firm and dry).
Now fill the dough into the prepared form and bake in the oven for about 20-25 minutes.