Mac and Cheese Soup is creamy and cheesy just like mac and cheese and if you're a mac and cheese lover (who isn't?), this soup is sure to become a favorite.
Cook pasta shells to al dente in salted water. They will cook a little more in the soup and absorb liquid from it, so be careful not to overcook.
Melt butter in a Dutch oven or large pot. Add celery and onion and cook until celery is soft.
Sprinkle flour on top of celery and onion. Stir it into the butter and cook 1 minute.
Gradually whisk in chicken broth and milk. Bring to a simmer. Add dry mustard, Worcestershire sauce, garlic salt, black pepper, and cayenne pepper. Continue to simmer until it thickens some.