Sponge Cake
Instructions
To prepare the sponge cake, separate the egg whites from the yolks (1) and put them in 2 separate large bowls (2); beat the yolks with half of the sugar (3) with a whisk, or a planetary mixer, until frothy, risen and light yellow (4).
Now clean the whisk well and beat also the egg whites (5) and, after about 5 minutes, when they're already quite risen and white, add the remaining sugar (6) and continue to beat for a few minutes more (the trick to test if egg whites are beaten until stiff is to tilt slightly the bowl you're using: if the mixture slides down, it means that it's not ready yet; , if it's stiff, on the contrary, it won't move inside the bowl).
Add the whisked egg whites to the whisked yolks (you can use a larger bowl) and at this point add the flour and the potato starch mixed together (7) (if you want also the vanilla powder), pouring them through a sifter to remove lumps.
Stir everything with a wooden spoon until homogeneous, but be careful it doesn't go runny.
Butter (8) and flour (9) well a 9-inch (24 cm) round springform pan (7-8) and pour the mixture into the centre of the mould, spreading it evenly (11).
Preheat the oven to 350F (180C) and bake your sponge cake for at least 35-40 minutes, never opening the oven door for the first half an hour of baking.
Take out the mould from the oven (12) and let the sponge cake cool down inside before opening.
