Heat the oil in a large oven-safe skillet over medium heat. Brown the beef with the onion for 5 to 6 minutes, then drain extra grease.

Stir in the garlic, broth, milk, macaroni, ketchup, mustard, salt, and pepper. Bring it to a simmer.

Cover and cook for 10 to 12 minutes, stirring twice, until the pasta is tender.

Stir in half the cheese. Sprinkle the rest on top, cover for 2 minutes, and let it melt.