Cake batter:

Whisk eggs and sugar well with a hand mixer until it is white, airy, and frothy, Mix flour, baking powder, and cocoa together and sift it into the egg mixture. Create a baking pan from baking paper, measuring 25x35 centimeters, and pour the batter into it. Bake the cake layer in a preheated oven at 225 degrees Celsius (437 degrees Fahrenheit) on the second lowest rack for 8-9 minutes. While the cake is in the oven, lay a piece of baking paper sprinkled with sugar ready on the table. When the cake is done, turn it out onto the sugar-sprinkled baking paper on the table. Take a cold and wet cloth (but not so wet that water runs) and wipe it over the baking paper. Carefully pull the baking paper off the cake layer - be cautious so the cake doesn't stick to the paper. Let the cake cool down for a few minutes.

Filling:

Whip the cream stiff. Cut the bananas into thin slices. Spread the whipped cream on the cake layer (save a bit for garnish) and place the sliced bananas on top of the whipped cream. Using the baking paper, roll the cake into a roll. Place the roll on a serving dish and garnish it with the remaining whipped cream.