Preheat oven to 300 degrees. In mixing bowl, cream butter. Add flour and sugar; mix just to combine (chill 10 minutes if too soft).
Pat into an 8-inch round cake pan; crimping edge with a floured fork. Bake until firm and slightly browned, 30 to 35 minutes (drape with foil if browning too quickly). Immediately score into eight wedges; cool completely. Turn out of pan; slice with a serrated knife.