Preheat your oven to 350°F.

Melt 2 tablespoons of butter in a large skillet over medium heat and add sliced onions, cooking until caramelized (about 20-25 minutes).

Reserve half of the caramelized onions for the gravy and mix the rest into a bowl with the ground beef, eggs, breadcrumbs, Worcestershire sauce, thyme, salt, and black pepper.

Gently fold the mixture to avoid overmixing.

Shape the mixture into a loaf and place it in a loaf pan or on a lined baking sheet.

Bake the meatloaf in the preheated oven for 45 minutes or until it reaches an internal temperature of 160°F.

In the meantime, prepare the onion gravy by returning reserved onions to the skillet, adding the last tablespoon of butter, and sprinkling in the flour, whisking for about one minute.

Slowly pour in the beef broth while whisking to avoid lumps and let it simmer for 5-7 minutes until it thickens.

Once the meatloaf is done, sprinkle shredded Swiss cheese and layer provolone slices on top, then broil for another 3-5 minutes until the cheese is bubbly and golden.

Let the meatloaf rest for 5-10 minutes, then slice and serve with warm onion gravy drizzled on top.