Slow-Cooker Mushroom Beef Stroganoff

Cut steak into 3x1/2-in. strips. In a 5- or 6-qt. slow cooker, combine next 9 ingredients. Stir in steak strips. Cook, covered, on low until meat is tender, 6-8 hours., Transfer steak to a serving dish; keep warm. Skim fat from cooking juices. Mix cornstarch and water until smooth; stir into cooking juices. Cook, covered, on high until thickened, 10-15 minutes. Stir in sour cream; pour over beef. Serve with noodles and, if desired, minced parsley.