Preheat your oven to 350°F (175°C).
In a large skillet, heat the olive oil over medium heat. Add the sliced onions and cook, stirring occasionally, until they are golden brown and caramelized, about 20 minutes.
Add the ground beef to the skillet with the onions and cook until browned, breaking it up with a spoon as it cooks.
Stir in the minced garlic, salt, pepper, and thyme. Cook for another minute until the garlic is fragrant.
Add the Worcestershire sauce and beef broth, stirring to combine. Bring the mixture to a simmer and let it cook for about 5 minutes.
Meanwhile, cook the pasta according to package instructions until al dente. Drain and set aside.
In a large casserole dish, combine the cooked pasta with the beef and onion mixture. Stir in the Swiss cheese.
Sprinkle the Parmesan cheese evenly over the top.
Bake in the preheated oven for 20-25 minutes, until the cheese is melted and bubbly.

Garnish with chopped parsley or fried French onions before serving.

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