Bake 4 hours or until turkey is done (170°F), uncovering after 3 hours. Remove turkey from pan; tent with foil. Let stand 15 min. before carving. Meanwhile, pour pan drippings into large measuring cup. Discard excess fat that rises to surface. If pan drippings are less than 2 cups, add enough water to drippings to measure 2 cups; pour into medium saucepan. Mix corn starch and water until blended; gradually stir into drippings. Bring to boil, stirring constantly; strain through fine mesh strainer.