Caramelize the onions: In a large skillet or Dutch oven, heat butter and olive oil over medium heat. Add sliced onions, salt, and sugar. Cook for 25–30 minutes, stirring occasionally, until the onions are deep golden brown and caramelized.

Add flavor: Stir in the garlic and thyme, cooking for 1–2 minutes. Deglaze the pan with balsamic vinegar and wine (if using), scraping up any browned bits.

Cook the pasta: Add the beef broth and bring to a boil. Add the pasta and stir well. Reduce heat to a simmer, cover, and cook for about 10–12 minutes, or until pasta is tender. Stir occasionally.

Make it creamy: Once the pasta is cooked and most of the liquid is absorbed, stir in the heavy cream and half of the cheese. Let it simmer for another 2–3 minutes until creamy.

Serve: Sprinkle the remaining cheese on top and let it melt. Garnish with fresh parsley and cracked black pepper. Serve warm.