In a skillet over medium heat, brown pork chops in oil. Place in a 13-in. x 9-in. baking pan. In a saucepan, combine orange juice, brown sugar, mace, ginger, salt if desired and pepper; bring to a boil. pour over chops. Cover and bake at 350° for 30 minutes. Peel potatoes; cut into 1/3-in. slices. Brush with butter. Turn chops. Cover with potatoes; baste with pan juices. Cover and bake 40 minutes longer or until potatoes are tender. Remove chops and potatoes to a serving platter; cover and keep warm. Dissolve cornstarch in water; stir into pan juices. Bring to a boil; boil for 2 minutes, stirring constantly. Pour over pork chops and potatoes.