Queen Mary's Sponge Cake
From 1931 Joy of Cooking (First Edition) Page 225

When King George was sick, his wife, who is reputed to have that inborn thing, "a light hand with pastry," brought him a volume of Marie Corelli's and baked a sponge cake for him. Who says that the lives of Queens are complicated?

This cake contains neither baking powder, nor cream of tartar, but depends for its lightness upon the air that is first beaten and then folded into it. This recipe makes a large, delicate, fine grained cake, which, if somewhat uninteresting, makes up for that by being highly digestible.

6 eggs
1 cup sugar
1 cup cake flour
Rind of 1 lemon
Juice of 1/2 lemon
1/4 teaspoon salt

1 teaspoonful of vanilla and 1 teaspoonful of water may be substituted for the lemon juice.

Separate the eggs and beat the yolks until they are light. Grate the lemon rind over the sugar, and add the sugar slowly to the egg yolks, stirring them briskly with a wire whisk. Add the lemon juice and when these ingredients are creamed, begin to fold in the egg whites, which have been whipped with the salt to a stiff froth. When the egg whites are partly folded in, begin adding the flour--one tablespoon at a time. Cut and fold lightly until the flour is blended, then pour the batter into an ungreased angel food pan and bake it in a slow oven 325 for one hour.