Step 1: Prepare the Onions

1. Sauté the Onions: In a large skillet, melt 2 tablespoons of butter over medium heat. Add the finely chopped onion and cook for about 10-15 minutes, stirring occasionally, until the onions are golden brown and caramelized. This step is crucial, as the sweet, rich flavor of the onions will elevate the meatballs to a whole new level!
2. Add Garlic: Once the onions are caramelized, add the minced garlic and sauté for an additional 1-2 minutes until fragrant. Remove the skillet from heat and let the mixture cool slightly.

Step 2: Make the Meatball Mixture

3. Combine Ingredients: In a large mixing bowl, combine the ground beef, breadcrumbs, Parmesan cheese, ricotta cheese, egg, thyme, salt, and pepper. Now, here’s a tip: don’t overmix! Gently combine the ingredients until just mixed to keep your meatballs tender.
4. Incorporate Onions: Once the onion and garlic mixture has cooled a bit, fold it into the meat mixture until well combined.

Step 3: Form the Meatballs

5. Shape the Meatballs: Using your hands, form the mixture into golf-ball-sized meatballs, about 1 to 1.5 inches in diameter. Place them on a baking sheet lined with parchment paper to keep them from sticking.

Step 4: Brown the Meatballs

6. Preheat Oven: Preheat your oven to 400°F (200°C).
7. Brown the Meatballs: In the same skillet used for the onions, add a bit more butter and heat over medium-high heat. Working in batches, add the meatballs and brown them on all sides, about 5 minutes total. Don’t worry if they’re not fully cooked through; they’ll finish cooking in the oven.

Step 5: Simmer the Meatballs

8. Add Beef Broth: Once the meatballs are browned, carefully pour in the beef broth. This will help keep the meatballs moist and flavorful while they bake.
9. Bake the Meatballs: Transfer the skillet to the preheated oven and bake for 15-20 minutes, or until the meatballs are cooked through and reach an internal temperature of 160°F (70°C).

Step 6: Add Cheese Topping

10. Melt the Cheese: Remove the skillet from the oven and sprinkle the shredded Gruyère or Swiss cheese evenly over the meatballs. Return to the oven and bake for an additional 5 minutes, or until the cheese is melted and bubbly.

Step 7: Serve and Enjoy!

11. Serving Suggestions: Let the meatballs rest for a few minutes before serving. This will allow the juices to redistribute, making them even juicier.