In a large bowl, combine the potatoes, bread cubes, onion, celery leaves, parsley, butter, salt and pepper. In a small bowl, beat flour and egg substitute. Stir in milk; pour into the potato mixture and mix well. Add more milk if filling seams dry. Just before baking, stuff the turkey. Skewer openings; tie drumsticks together. Place on a rack in a roasting pan. Bake at 325 deg; for 4-1/2 to 5 hours or until a meat thermometer reads 180 deg; for the turkey and 165 deg; for the stuffing. When turkey begins to brown, cover lightly with a tent of aluminum foil and baste if needed. Remove all stuffing. Editor's Note: Stuffing may be baked in a greased 3-qt. covered baking dish at 325 deg; for 70 minutes (uncover for the last 10 minutes). Stuffing yields about 10 cups.