Preheat the oven to 180 ° C.
Separate the white from the yolks.
Blanch the sugar with the egg yolks.
Add the flour, cornstarch and butter.
Beating egg whites.
Incorporate into the preparation.
Pour onto a baking sheet lined with baking paper. Roll out to get a nice rectangle with the same thickness over the entire surface.
Bake for about 12 minutes.
Immediately after removing from the oven, place a new sheet of baking paper on the sponge cake and turn over on a new baking sheet.
Gently remove the sheet of baking paper that was used for cooking.
Gently roll the sponge cake with the new sheet of paper. Cover with a cloth. Then let cool.