Bring a large pot of salted water to a boil. Add the spaghetti or fettuccine and cook according to package instructions until al dente. Reserve 1/2 cup of pasta water, then drain and set aside.

In a large skillet over medium heat, add the ground beef. Cook until browned, breaking it apart with a spoon. Drain excess grease if necessary.

Add butter to the skillet with the beef. Once melted, add the minced garlic and red pepper flakes (if using). Sauté for 1-2 minutes until the garlic is fragrant, being careful not to burn it.

Pour in the beef broth and bring to a simmer. Allow it to reduce slightly for about 3-4 minutes.

Add the cooked pasta to the skillet, tossing to coat the pasta with the garlic butter mixture. If the sauce is too thick, add reserved pasta water a little at a time until reaching the desired consistency.

Stir in the grated Parmesan cheese and season with salt and pepper to taste. Toss everything together until well combined and the cheese has melted.

Plate the Garlic Butter Beef Pasta and garnish with fresh parsley. Enjoy immediately!