01 -
Layer the sliced onions evenly across the bottom of your 6-quart slow cooker, then add the frozen meatballs on top.
02 -
In a medium mixing bowl, combine the beef broth, gravy mix, minced garlic, black pepper, thyme, and white wine vinegar. Whisk everything together until smooth, then pour this mixture over the meatballs.
03 -
Cover your slow cooker and cook on high heat for 2½ to 3½ hours, or switch to low heat and cook for 5 to 6 hours until the meatballs are heated through and the onions are tender.
04 -
In a small bowl, whisk the cornstarch with cold water until completely smooth. Stir this mixture into the meatballs, then sprinkle the grated gruyere cheese evenly over the top. Cook for an additional 10 minutes until the cheese melts beautifully.
05 -
Serve these cheesy meatballs over fluffy rice, creamy mashed potatoes, or buttered noodles for a complete meal.