Sponge Cake

From 1910:

Equal parts of eggs and sugar by weight;
half the weight of the eggs in sifted flour.

To one pound of eggs, use the grated rind and juice of one large, fresh lemon.
Beat the yolks and whites separately, very stiffly, before adding flour to both. Beat until perfectly smooth,
with up and down strokes, and bake on sheets of tin immediately, in a quick, but not too hot, oven.