Directions:
1. Preheat your oven to 375°F (190°C).
2. In a large skillet, heat the butter and olive oil over medium heat. Add the sliced onions and cook, stirring occasionally, until they are caramelized, which should take about 20-25 minutes.
3. Once the onions are caramelized, add the beef broth and cook until it has reduced by half. Remove the skillet from the heat and let the mixture cool.
4. In a large bowl, combine the ground beef, breadcrumbs, Gruyere cheese, eggs, minced garlic, Worcestershire sauce, dried thyme, salt, and pepper. Mix everything until it is well combined.
5. Stir in the cooled caramelized onions.
6. Shape the mixture into a loaf and place it in a greased baking dish.
7. Bake the meatloaf in the oven for 1 hour, or until it is cooked through and the internal temperature reaches 160°F (71°C).
