In a large Dutch oven or deep skillet, melt 2 tablespoons of butter over medium heat. Add the finely diced onion and cook until translucent and soft, about 3-4 minutes.

Add the ground beef, breaking it apart with a wooden spoon. Cook until browned and no pink remains, about 5-6 minutes. Drain excess fat if necessary.

Push the beef to the sides and add the remaining 2 tablespoons of butter and minced garlic to the center. Cook for 1 minute until fragrant, stirring to combine with the beef.

Stir in the beef broth and Italian seasoning, scraping any browned bits from the bottom of the pot. Add red pepper flakes if using.

Add the dry pasta, ensuring it's mostly submerged. Bring to a gentle boil, then reduce to a simmer. Cover and cook for 10-12 minutes, stirring occasionally, until the pasta is al dente and most liquid is absorbed.

Remove from heat and stir in the heavy cream and Parmesan cheese until the sauce is creamy and thickened.

Taste and season with salt and pepper as needed. Garnish with chopped parsley and serve hot.