Preheat the oven to 190 degrees. Line the muffin tray with 12 paper muffin cups. Mix the flour with the baking powder and spices. Beat the soft butter with the sugar until fluffy and then mix in the eggs well. Mash the bananas with a fork and roughly chop the walnuts. Stir the flour mixture into the foam mixture with a spatula.
Then stir in the mashed bananas and add the walnuts. Stir everything briefly.
Pour the batter into the muffin tins and bake at 190 degrees for about 20 minutes on the middle rack. Test with chopsticks, if nothing sticks, then the muffins are ready.
If you want, you can add a chocolate glaze on top.