Sift the flour, baking powder, and cocoa if you're making a chocolate sponge cake.

Butter the mold, flour it, and line the bottom with a round of parchment paper.

Preheat oven to 175°C / 350°F

In the bowl of the stand mixer, put the eggs, sugar, and vanilla sugar. Beat for 5 minutes at maximum speed (speed 10).

You can do this step with a hand mixer, but it will take a little longer.

The mixture should triple in volume, become white and creamy.

Add the sifted flour in three batches, gently incorporating it with a spatula, from bottom to top, to avoid deflating the mixture.

Pour immediately into the mold, then put in the oven. Bake between 30 and 45 minutes.

Do not open the oven before the end of baking, as the sponge cake may collapse.

For me, it's perfectly cooked after 40 minutes. A skewer inserted in the center should come out dry.

Small tip: some ovens cook faster than others. For your first attempt, start monitoring the baking from 25 minutes, then adjust for the next times.

When out of the oven, run a knife around the sponge cake to loosen it from the sides of the mold.

Gently unmold onto a wire rack and let cool completely before wrapping in plastic wrap or cutting into 2 or 3 layers depending on its height.