Preheat your oven to 375°F (190°C).
In a skillet, melt the butter over medium heat and sauté the onions for 15-20 minutes until caramelized, stirring occasionally. Add the garlic during the last 2 minutes of cooking. Remove from heat and let cool slightly.
In a large mixing bowl, combine the ground beef, breadcrumbs, milk, egg, Worcestershire sauce, Dijon mustard, dried thyme, salt, and pepper. Add half of the caramelized onions to the mixture and stir until combined.
Shape the meat mixture into a loaf and place it in a greased loaf pan.
Pour the beef broth over the top of the meatloaf and bake for 45 minutes.
Remove from the oven, top with the remaining caramelized onions and shredded Gruyère or Swiss cheese.
Return to the oven and bake for an additional 10-15 minutes until the cheese is melted and bubbly.
Let the meatloaf rest for 10 minutes before slicing and serving.
Prep Time: 20 minutes | Cooking Time: 60 minutes | Total Time: 80 minutes
Servings: 6 servings | Kcal: 380 kcal per serving
