Put the eggs, sugar, salt, and lemon zest in the bowl of your mixer.

Beat them until very fluffy and pale yellow (about 15/20 minutes on medium/high speed). To test that it has been beaten enough, let a small amount of batter fall into the bowl. If it remains "sitting" on top, it means that it's ready.

Sift the flour on top of the egg mixture, a little at a time, and fold it gently with a wooden spoon.

Pour the batter into the prepared pan (buttered pan and sprinkled with cornstarch or a silicone mold or a baking sheet lined with parchment paper). Don't smooth the top or bang the pan on the counter, leave it as it is!

Bake for 40 minutes at 160°C or until a toothpick inserted into the center comes out clean.

Turn off the oven but leave the cake inside (keep the door slightly open using a wooden spoon) for 5/10 minutes so it can cool down slowly.

Remove the sponge cake from the oven, let it cool before using it.