Preheat oven to 375℉.
In a large skilled, heat butter and olive oil over medium heat.
Add sliced onions and cook, stirring occasionally until caramelized, about 20-25 minutes.
Add beef broth and cook until reduced by half. Remove from heat and let cool.
In a large bowl, combine ground beef, breadcrumbs, cheese, eggs, garlic, Worcestershire sauce, thyme, salt, and pepper. Mix until well combined.
Stir in the cooled caramelized onions.
Shape the mixture into a loaf and place it in a greased baking dish.
Bake for 1 hour, or until the meatloaf is cooked through and the internal temperature reaches 160℉.
Let rest for 10 minutes before slicing and serving.