In a large saucepan, cook the ground beef, onion and garlic until the beef is browned.
Mix in the salt, Italian seasoning, crushed red pepper flakes and spinach. Add in the milk, beef broth, macaroni and pasta sauce. Bring to a boil, then reduce heat. Allow to simmer for 12-15 minutes, stirring often.
Mix in the cheese until melted. Allow to sit for around 5 minutes, then serve immediately.