Directions

1. Cook pasta according to package instructions; drain and set aside.
2. In a large skillet, heat butter and olive oil over medium heat.
3. Add onions and cook slowly until deeply caramelized, about 20 minutes.
4. Add garlic and cook 1 minute more.
5. Pour in beef broth; simmer 5 minutes to reduce slightly.
6. Stir in cheeses until melted and sauce is creamy.
7. Add cooked pasta to skillet; toss to coat evenly.
8. Season with salt, pepper, and fresh thyme if using.
9. Serve hot with extra cheese sprinkled over.