Cut partially frozen steak into 3-inch strips about 1/2" wide.
Combine 1/2 cup flour, salt, pepper, dry mustard and thyme leaves; toss with steak strips to coat thoroughly.
Place coated steak strips in CrockPot; stir in onion rings and mushrooms.
Add beef broth, wine and Worcestershire Sauce; stir well.
Cover and cook on Low setting for 8 to 10 hours.
Before serving, combine sour cream with 1/4 cup flour; stir into CrockPot.
Serve Stroganoff over hot buttered noodles; garnish with minced parsley.