01 -
Place frozen beef meatballs in a single layer at the bottom of a 4-6 quart slow cooker.
02 -
Pour French onion soup over the meatballs. Sprinkle beefy onion soup mix evenly over the top. Pour in beef broth.
03 -
Cover and cook on high for 2 to 3 hours or on low for 5 to 6 hours until heated through and flavors meld.
04 -
In a small bowl, whisk cold water and cornstarch until smooth to create a slurry.
05 -
Stir slurry into meatballs mixture, combine well, then cover and cook for an additional 10 minutes.
06 -
Sprinkle shredded mozzarella cheese evenly on top and cover until cheese melts, about 5 minutes.
07 -
Serve meatballs topped with fresh thyme if desired, alongside mashed potatoes, egg noodles, or crusty bread to soak up the broth.