Separate the whites from the yolks and mix them into stiff snow.
Add sugar and vanilla sugar and mix well again.
Then add the egg yolks one by one and mix the mixture after each one.
Add flour and baking powder and then mix the mixture by hand with a whisk.
Take the oven-sized pan and put baking paper on it.
Take a little of the mixture with a spatula or something similar and use it to stick the paper on the bottom side to the waterproofing so that it doesn't move.
Shake the mixture into the pan and level it well.
The biscuit is baked in an oven preheated to 350 degrees F for 15 minutes.
While the biscuit is baking, wet a cloth and wring it out well and spread it on the base.
Transfer the baked hot biscuit immediately to a cloth with the baking paper facing up.
Carefully separate the baking paper from the biscuit, and roll the biscuit together with a wet cloth.
Close the cloth on both sides and let the biscuit cool to room temperature.
Unwrap the cooled sponge cake, spread the jam evenly over the entire surface and carefully roll it up again.
Before cutting and serving, sprinkle with powdered sugar.