3oz castor sugar
1 1/2oz cornflour
1/2 t baking powder
Beat egg whites with salt until stiff. Add yolks and sugar and beat until thick and creamy and sugar is dissolved. Fold in sifted dry ingredients. Have ready a sponge roll tin buttered and floured. Pour in batter and spread evenly. Bake 14 minutes at 200C. Turn out on a dry cloth. Spread with boiling jam. Roll in cloth and leave until cold.
Source: Rally cook book, page 47