Mix flour, baking powder, cocoa, almonds and chocolate. Peel the bananas. Mash 2 bananas finely with a fork. Cut the remaining bananas into good 1⁄2 cm thin slices. Cream butter, sugar, vanilla sugar and 1 pinch of salt with the whisk of the mixer.
Stir in the eggs one by one. Stir in flour mixture in 2 portions.
Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Line a box cake tin (approx. 25 cm long; 1 3⁄4 l capacity) with baking paper. Stir the mashed bananas into the dough.
Carefully fold banana slices, up to 14 pieces, into the dough. Fill the dough into the tin, smooth it down and cover with the remaining banana slices.
Bake in a hot oven for 85-90 minutes. After about 45 minutes baking time cover with aluminium foil. Then take the cake out of the oven and let it cool on a cake rack in the tin for about 45 minutes. Lift out of the tin and let it cool down.