Roughly chop the nuts. Peel bananas and crush them with a fork. Apple wash, peel, cut into slices from the core, dice slices finely. Beat the eggs, 100 g sugar and oil. Stir in nuts, bananas and apples.
Mix flour, salt, cinnamon and baking powder. Quickly stir into the egg mixture. Stir in buttermilk.
Pour into a greased and floured box mould (30 cm; 2 litres capacity). Bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 50 minutes.
Take the cake out of the oven, let it rest in the mould for about 15 minutes and then turn it out of the mould. In the meantime caramelise 150 g sugar in a pot. Add crème fraîche and simmer until the caramel is dissolved.
Spread the finished caramel on the fallen cake. Decorate with banana slices if desired.