Génoise cake

Génoise. A sponge cake. The distinguishing feature of this type of cake is the only leavening is egg, there is no baking powder like an ordinary cake to make it puff up.  And there is very little flour, just enough to stiffen eggs blended with sugar into a ultra smooth exceedingly light batter. It is a whole-egg meringue stiffened with flour and flavored with butter and anything else you like, the simplest being with vanilla extract. And salt. That's it.

6 eggs

1 + 1/3 cup sifted flour (substitue a few tablespoons corn starch if you like, cake flour is best, but a/p flour is okay.

1/4 cup warm butter

1 teaspoon vanilla extract

1/2 teaspoon salt

There is no point in making a génoise, they're fine as far as sponge cake goes but boxed cake is better. 

The butter is browned and clarified and kept warm almost hot with the vanilla. 

The eggs are whipped with sugar very warm almost hot. 

The flour is best sifted twice and measured after sifting. 

It is also treated as a soufflé.