Cream butter and sugar until the consistency of whipped butter. Add flour, a cup at a time, and mix thoroughly after each addition.

Roll out dough on a floured pastry cloth to a thickness of 1/2-inch. Cut into 1-inch squares and place on baking sheet, leaving a little space between squares. Prick tops with fork.

Bake in a slow (275°F) oven for about 45 minutes or until lightly browned. Do not overbrown.

While still hot, sprinkle top of shortbread with extra-fine granulated sugar.

Makes 10 1/2 dozen cookies.