Grease a box mould (approx. 25 cm long; approx. 1 1/2 l capacity) and sprinkle with 2-3 tbsp. sugar. Coarsely chop 100 g nuts. Mix eggs, 100 g sugar, vanilla sugar and oil with the whisk of the hand mixer.
Mix flour, baking powder, 1 pinch of salt and cinnamon. Alternately stir into the egg-sugar mixture with the buttermilk. Peel and slice the bananas. Fold in with chopped nuts.
Fill the dough into the mould. Lightly press in the rest of the nuts. Bake in the preheated oven (electric oven: 175 °C/circulating air: 150 °C/gas: level 2) for 50-60 minutes.
Leave in the mould for about 15 minutes. Then turn over and let it cool down completely. Dust with icing sugar.