Brown the beef and onion in a large pot over medium heat. Drain extra grease.

Stir in the broth, milk, macaroni, ketchup, mustard, and salt.

Bring the mixture to a boil, then reduce the heat.

Cover and cook for 10–12 minutes. Stir often so the noodles do not stick.

Turn off the heat and stir in the cheese until smooth.