Potato-Flour Sponge Cake

5 egg whites 1-1/2 c. sugar 1/2 c. water 2/3 c. potato flour 1/3 c. wheat flour 1/2 tsp. cream of tartar 1 tsp. lemon extract

Beat the egg whites until stiff. Cook the sugar and water until the sirup threads.
Add this sirup to the egg whites and beat well. Sift the potato flour, wheat flour, and cream of tartar three times, and then fold into the mixture.
Add the flavoring, turn into a pan, and bake for about 40 minutes.