Instructions:

Brown the Beef:

In a large pot or Dutch oven, brown the ground beef over medium-high heat, breaking it apart with a spoon as it cooks.
Drain any excess grease.
Add Onion and Garlic:

Add the chopped onion and minced garlic to the pot and cook until softened, about 5 minutes.
Add Pasta and Broth:

Add the fettuccine pasta and beef broth to the pot.
Bring to a boil, then reduce heat to a simmer.
Cook the Pasta:

Cook the pasta according to package directions, stirring occasionally, until the pasta is al dente and most of the liquid has been absorbed.
Make the Sauce:

Stir in the milk or heavy cream, Parmesan cheese, and butter.
Cook for 2-3 minutes, stirring constantly, until the sauce has thickened slightly.
Season and Garnish:

Season with salt and pepper to taste.
Stir in the chopped parsley.
Serve:

Serve hot, garnished with additional Parmesan cheese and parsley if desired.