Step 1: Prepare the Onions and Meatballs. Start by placing the sliced onions in the bottom of a 6-quart crock pot, spreading them out evenly so they can caramelize beautifully as they cook. Then, pour the frozen meatballs over the onions, ensuring they are well distributed.
Step 2: Mix the Broth Ingredients. In a medium bowl, combine the low-sodium beef broth, brown gravy mix, minced garlic, black pepper, dried thyme, and white grape juice vinegar. Whisk these ingredients together until fully combined, then pour this flavorful mixture over the meatballs.
Step 3: Cook in the Crock Pot. Cover the crock pot and cook on high for 2½-3½ hours or on low for 5-6 hours until the meatballs are heated through and flavors meld beautifully together.
Step 4: Thicken the Sauce. In a small bowl, whisk together cornstarch and water until smooth. Pour this mixture over the meatballs in the crock pot and stir gently to combine everything thoroughly.
Step 5: Add Cheese and Finish Cooking. Top the mixture with grated gruyere cheese, then cover the crock pot again and cook for an additional ten minutes or until the cheese is melted and bubbly.
Step 6: Serve and Enjoy! Once ready, serve your delicious Crock Pot French Onion Meatballs over rice or mashed potatoes for a comforting meal that's sure to please!