In a large mixing bowl, combine ground beef with your favorite seasonings, such as salt and pepper. Form the mixture into bite-sized meatballs, about 1.5 inches in diameter. Heat a skillet over medium-high heat, add olive oil, and sear the meatballs for 6-8 minutes until they are browned on all sides. Remove the meatballs from the skillet and set them aside.

Using the same skillet, reduce the heat to medium-low and add a bit more olive oil if needed. Add thinly sliced onions and sprinkle a touch of sugar to aid caramelization. Sauté the onions for about 20 minutes, stirring occasionally, until they become deeply golden and soft.

Once the onions are perfectly caramelized, pour in beef broth and optional red wine. Stir well to combine all the flavors, scraping up any browned bits from the bottom of the skillet. Bring the mixture to a simmer over medium heat, allowing it to cook for about 5 minutes until slightly thickened.

Gently return the browned meatballs to the skillet, nestling them into the sauce. Spoon some of the sauce over the meatballs to infuse them with flavor. Let everything simmer together for an additional 5-10 minutes on low heat.

Sprinkle a generous layer of grated Gruyère cheese over the meatballs and sauce, and cover the skillet with a lid. Cook for 3-5 minutes on low heat, or until the cheese is bubbly and melted.