Peel the bananas, cut them into pieces and put them into a tall mixing bowl with lemon juice. Puree finely. Cream butter, vanilla sugar and sugar with the whisk of the hand mixer. Stir in the eggs one after the other. Mix flour and baking powder and stir into the dough alternately with the banana puree. Spread half of the dough on the greased fat pan of the oven (approx. 27 x 40 cm). Stir the cocoa under the other half and spread it on the light-coloured dough.
Pull through spirally with a fork. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 30 minutes (stick test). Remove and let cool on a cake rack. Dust with icing sugar and cut into pieces. Decorate pieces with banana slices and sliced chocolate. Whipped cream tastes good with it
Waiting time approx. 1 hour