Chop 100 g chocolate coating, melt over a warm water bath. Mix flour, sugar, baking powder, baking soda, salt and vanilla sugar. Peel 2 bananas and puree the pulp with 100 ml oil and yoghurt. Add eggs and banana puree to the flour mixture and stir in briefly.
Put about half of the dough into a greased, flour-blown box form (approx. 25 cm long, 1.7 litres capacity), smooth it down. Spread half of the chocolate coating on top. First add the remaining dough, then the remaining chocolate coating. Pull a fork briefly through the dough in a spiral shape. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for 45-50 minutes. Remove from the oven, leave to rest in the form for approx. 5 minutes, then turn out. Place the cake on a cake rack and let it cool down.
Chop 200 g chocolate coating, melt with 2 tablespoons of oil over a warm water bath. Peel 2 bananas and halve them lengthwise. If necessary, straighten the cake a little on the surface. Place banana halves on top. Spread the chocolate on top and let it dry. Whipped cream tastes good with it.