6 eggs
1/3 teaspoon cream of tartar
1 cup sugar
3/4 cup flour
1 teaspoon freshly squeezed lemon juice
1 teaspoon pure vanilla

Preheat oven to 350°F.

Have the eggs at room temperature. Separate the eggs. Beat the yolks with a rotary beater until they are thick and lemon colored. Using a clean bowl and beaters, beat the egg whites until they are foamy, add the cream of tartar and continue beating until they had dry.

Fold the sugar into the egg whites and then fold the yolks into this mixture. Sift the flour several times and add it. Add the lemon juice and vanilla, pour into an ungreased sponge cake pan, and bake in preheated oven until a toothpick inserted in the center of cake comes out clean.