Alternately, in a medium bowl, sift or whisk together flour, cornmeal, granulated sugar, and salt. Using your fingers, cut in cold butter until mixture resembles coarse crumbs and butter is pea-size. Make a well in center, and add cold milk. Stir with fingers just until dry ingredients are moistened. Turn out dough, and shape into a disk. Wrap in plastic wrap, and refrigerate for at least 1 hour.