1. Add the frozen meatballs to the bottom of a 6 quart slow cooker. Scatter the baby carrots, sliced celery, and diced onion evenly over the top.

2. In a medium bowl whisk together the beef broth, tomato paste, Worcestershire sauce, soy sauce, garlic powder, onion powder, dried thyme, salt, and black pepper until the tomato paste is fully dissolved.

3. Pour the gravy mixture evenly over the meatballs and vegetables, pressing everything down gently so most of it is submerged in the liquid.

4. Cover and cook on LOW for 4 to 6 hours or on HIGH for 2 to 3 hours, until the vegetables are tender and the meatballs are heated through and very soft.

5. In a small bowl stir together the cornstarch and cold water until smooth. Stir this slurry into the slow cooker, cover again, and cook on HIGH for 15 to 20 minutes, until the gravy has thickened to your liking.

6. Taste the gravy and adjust seasoning with additional salt and pepper if needed. If it becomes too thick, thin with a splash of broth or water.

7. Spoon mashed potatoes, rice, or egg noodles into bowls and ladle the meatballs, vegetables, and plenty of gravy over the top. Serve hot.