In a large pot, melt the butter over medium heat and add the thinly sliced onions. Cook them, stirring frequently, for about 15-20 minutes until they turn a lovely golden brown and become caramelized.

Once the onions are beautifully caramelized, stir in the minced garlic and cook for an additional minute until fragrant.

Pour in the beef broth, then add the thyme and bay leaf. Bring the mixture to a gentle simmer, letting the flavors meld together for about 5 minutes.

Add your desired pasta to the pot, ensuring it's submerged in the broth. Cook according to the package instructions, usually around 10-12 minutes, stirring occasionally.

Once the pasta is cooked and the liquid is mostly absorbed, remove the pot from heat. Stir in the Gruyère cheese until it's melted and creamy.

Discard the bay leaf, then spoon the pasta into bowls. Garnish with freshly chopped parsley for a fresh touch and serve warm.