French Onion Meatballs

Preheat the oven to 375ºF. Line a baking sheet with parchment paper. Set it aside.

To make the meatballs, in a large bowl, combine the ground beef, breadcrumbs, egg, and Gruyère cheese. Stir in the Worcestershire sauce, thyme leaves, and garlic. Season with salt and pepper to taste.

Using hands or a cookie scoop, shape the meatballs and arrange them on the baking sheet. Bake until they are golden and cooked through, about 20 to 25 minutes.

While the meatballs are baking, to make the French onions, in a large oven-safe skillet, melt the butter over medium-high heat. Add the onions to the skillet and season with salt and pepper to taste. Reduce the heat to medium and cook, stirring occasionally, until the onions are golden brown, about 20 to 25 minutes. Stir in the beef broth, Worcestershire sauce, Dijon mustard, and thyme leaves. Season with salt and pepper to taste. Bring the mixture to a simmer. Transfer the meatballs to the pan and continue to cook until the liquid begins to reduce, about 5 minutes.

Top the meatballs with the remaining Gruyère cheese and broil in the oven until the cheese is melted and golden, about 1 to 2 minutes.

Serve immediately or store in the refrigerator for up to 3 days.