1- Place the 2 sliced medium yellow onions at the bottom of a 6-quart slow cooker. This creates a flavorful bed.

2- Add 26 ounces of frozen plain-flavored meatballs on top of the onions.

3- In a bowl, whisk 2 cups low-sodium beef broth, 1 ounce brown gravy mix, 2 teaspoons minced garlic, 1 teaspoon black pepper, 1 teaspoon dried thyme, and 1 tablespoon white wine vinegar. Pour over the meatballs.

4- Cover and cook on high for 2½ to 3½ hours or low for 5 to 6 hours, until heated through and flavors meld.

5- Mix 2 tablespoons cornstarch with ¼ cup water to form a slurry. Stir into the slow cooker to thicken the sauce.

6- Sprinkle 1½ cups grated Gruyere cheese on top. Cover and cook for an additional 10 minutes until melted.

7- Serve hot over rice, mashed potatoes, noodles, or vegetables. Crusty bread is great for dipping.