Roughly chop the walnuts. Cream fat, sugar and 1 pinch of salt with the whisk of the hand mixer. Stir in the eggs one after the other. Alternately add flour, baking powder and buttermilk to the mixture. Halve the dough.
Peel banana and cut it roughly into pieces. Peel apple, quarter it, remove seeds and halve it again. Cut into small pieces and sprinkle with lemon juice. Grease a box mould (approx. 1 litre capacity) and a ring cake mould (approx. 1 litre capacity) and sprinkle with sugar. Fold the apple pieces under one half of the dough and fill into the ring cake tin. Stir banana pieces and 1 pinch of cinnamon into the other half and fill into the tin. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for about 45 minutes. Remove from the oven and place on a cake rack. After about 15 minutes, remove from the mould and allow to cool.
Fold the apple pieces under one half of the dough and fill into the ring cake tin. Stir banana pieces and 1 pinch of cinnamon into the other half and fill into the tin. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for about 45 minutes. Remove from the oven and place on a cake rack. After about 15 minutes, remove from the mould and allow to cool. Chop banana chips and walnuts and decorate banana bread with them