Add milk, cream, salt, dry mustard, pasta and butter into a medium sized pan. over medium heat.
Bring the mixture to a simmer, stirring frequently. Once at a simmer, turn heat down to low.
Cook and stir frequently for about 20 minutes, until most of the liquid is absorbed. Add 1/4 cup more milk if pasta is not fully cooked and continue cooking until pasta is al dente.
Remove from heat and stir in cheeses. Cover and let stand for at least five minutes for the cheese sauce to set.
Serve immediately, garnished with fresh minced parsley if desired.
Notes
Mix and match any of these cheeses for an amazing flavor: Parmesan, Sharp Cheddar, White Cheddar, Jack cheese, Gouda, Gruyere, Fontina, Blue Cheese, Gorgonzola, Mozzarella, Pepper Jack, Colby Jack, or Swiss.