In a large bowl, put the egg yolks (keep the whites aside), the sugar, the melted butter, the vanilla, and half the flour. Mix well.
Then beat the egg whites with a pinch of salt.
Add two tablespoons of egg whites to the bowl with the rest of the ingredients. Gently fold in.
Then add the other half of the flour. Mix well to incorporate all the flour. If necessary, add the almond powder at this stage.
Finally, gently fold in the egg whites.
Turn on the oven to 180°C.
Cover a rectangular dish (18 x 13 cm in my case) with baking paper. Then pour in the sponge cake mixture.
Bake for about 8 and a half minutes at 180°C. The biscuit should be barely golden.
Remove from the oven immediately and take the sponge cake out of the dish.
Brush the biscuit with cold espresso (to which you can add a tablespoon of rum or amaretto) or a spray, so that the biscuit is soaked (you can also put the coffee in a dish and dip the sponge very quickly in it, but be careful not to get it too wet).
Roll the sponge cake up very carefully and gently so as not to damage it, without removing the baking sheet. Cover the sponge cake with a damp cloth and keep it aside while you prepare the rest of the cake.