Preheat the oven at 250 degrees Celsius.
Mix the eggs and sugar with an electrical mixer. While stirring add the cacao powder, potato flour, baking powder and flour.
Place a baking paper on a baking sheet and pour the batter on the paper. Place in the middle of the oven for 5 minutes.
On a baking paper sprinkle sugar. Take out the cake from the oven and place it upside down on the paper with sugar.
When the cake is cold take it away from the paper. If the cake is stuck, brush the paper with cold water.
Whip the whip cream and the vanilla sugar together.
Mash the bananas with a fork. Mix it together with half of the whip cream.
Place the banana mixture evenly on the cake. Roll the cake together from the long side.
Place the rest of the whipped cream on top of the cake. Sprinkle the grated chocolate on top.