Sift the flours together and add, gradually, with the sugar to the butter. Knead to a soft dough. Shape into medium-thick, round cakes the size of a saucer, place on rimmed, greased cookie sheets, prick with a fork and flute the edges. (For modern consumption the shortbread may be more useful cut in cookie size squares or diamonds or in fancy shapes.) Bake in a 400 degree F oven for 30 minutes.