Stir together first 3 ingredients in a medium bowl; cut in butter with a pastry blender until crumbly. (Mixture will look very dry.) Gently press mixture together with hands, working until blended and smooth (about 2 to 3 minutes).
Shape dough into 2 (4-inch-long) logs. Wrap in plastic wrap, and place in an airtight container. Chill 8 hours, or freeze up to 3 months. (Thaw overnight in refrigerator.)
Cut into 1/4-inch-thick slices, and place on a lightly greased baking sheet. Brush with milk.
Bake at 350 degrees for 12 to 15 minutes or until lightly browned.Freeze up to 1 month, if desired.
Comments: Dough may be rolled into a 10- by 7-inch (1/4-inch-thick) rectangle on a lightly floured surface. Cut lengthwise into 8 strips and crosswise into 4 strips, using a pastry wheel or knife and forming 32 squares. Place cheese squares on a lightly greased baking sheet, and bake immediately.