Add the frozen meatballs to the slow cooker.

In a separate bowl, combine the beef broth, onion soup mix, brown gravy mix, ketchup, and Worcestershire sauce.

Whisk until well combined, then pour the mixture over the meatballs.

Cover and cook on low for 5-6 hours or on high for 3-4 hours.

Before serving, whisk together the cornstarch and cold water until smooth, then stir into the gravy.

Cover and cook on low for an additional 10 minutes, or until the gravy has thickened.

Serve warm over mashed potatoes, rice, or egg noodles.