Caramelize the onions: In a large pot or Dutch oven, heat the olive oil over medium heat. Add the sliced onions and cook, stirring occasionally, for 15-20 minutes until the onions are soft, golden brown, and caramelized. Be patient—this step is key for developing the deep, rich flavor. If the onions start to burn, lower the heat.

1. Add garlic and herbs: Add the minced garlic to the caramelized onions and cook for another 1-2 minutes until fragrant. Stir in the dried thyme, rosemary (if using), salt, and pepper to season the mixture.
2. Cook the pasta: Pour in the beef broth and water, stirring to combine. Bring the mixture to a simmer, then add the pasta. Stir to ensure the pasta is submerged in the liquid. Cover the pot and cook the pasta for 10-12 minutes, stirring occasionally, until the pasta is al dente and the liquid is mostly absorbed. If the pasta seems too dry, add a bit more water or broth as needed.
3. Finish the sauce: Once the pasta is cooked, reduce the heat to low. Stir in the heavy cream and grated Parmesan cheese, and cook for an additional 1-2 minutes until the sauce is creamy and well combined.
4. Add the cheese: Sprinkle the shredded Gruyère cheese over the pasta and stir until the cheese is melted and the pasta is coated in a creamy sauce. Taste and adjust the seasoning with salt and pepper if needed.
5. Serve: Serve the pasta hot, garnished with fresh parsley and additional Parmesan cheese if desired.