Preheat oven to 180°C
Sift together flour, baking powder, cinnamon, and salt. Set aside
Cream sugar with butter until light and fluffy.
Add eggs to the creamed butter & sugar one at a time and beat in. Then mix in the crème fraîche, vanilla extract and mashed bananas.
Fold in the flour mixture, a third at a time. Then fold in the toasted walnuts.
Place a knob of butter into a 28 cm x 12 cm loaf pan and place into the preheated oven until the butter melts (about 15 seconds). Remove pan from oven and coat the pan with the melted butter, using a pastry brush.
Pour the batter into the loaf pan and bake for 50 minutes to an hour in preheated oven. Check for doneness with a cake tester - once it comes out clean the cake is ready. Allow to cool for 5-10 minutes in the pan. Best served warm with a strong espresso.