Place the stew beef in your Crock Pot.
In a bowl, mix together the onion soup mix, cream of mushroom soup, beef broth, Worcestershire sauce, garlic powder, and black pepper.
Pour the mixture over the beef.
Cover and cook on low for 7-8 hours or on high for 4-5 hours until the beef is tender.
In a small bowl, combine cornstarch and cold water until smooth. Stir into the Crock Pot.
Cook on high for an additional 30 minutes or until the gravy thickens.
Serve hot over mashed potatoes, rice, or egg noodles.