In a large pot, melt 4 tablespoons of unsalted butter over medium heat. Add 3 sliced large yellow onions with a pinch of salt. Cook for 20-25 minutes, stirring occasionally, until golden brown and caramelized.

Pour in 4 cups of low-sodium beef broth and add a few sprigs of fresh thyme. Bring to a gentle simmer for about 10 minutes.

While the broth simmers, boil salted water in a separate pot. Cook your favorite wide pasta until al dente, around 8-10 minutes. Reserve 1 cup of pasta water before draining.

Once the pasta is ready, add it to the pot with the onion and broth mixture. Stir well to combine, adding reserved pasta water if too thick.

Preheat your broiler to high and transfer the pasta mixture to an oven-safe dish. Sprinkle 2 cups of shredded Gruyère cheese on top.

Broil for 3-5 minutes until the cheese is bubbly and golden brown. Remove from oven and let cool slightly before serving.

Serve generous portions on plates and enjoy with a salad or crusty bread.