Place uncooked pasta, milk, salt and pepper in large stockpot. Over medium to medium-high heat, bring mixture to low simmer (this will take a few minutes), stirring regularly to prevent sticking. Once simmering, cook 3-5 minutes or until pasta is al dente, stirring constantly to prevent sticking. If necessary, adjust heat to keep at a low simmer.
When pasta has reached al dente, remove from heat and stir in cheeses. Mix until combined and melted. Taste and adjust seasonings if necessary. Garnish with parsley and red chili flakes if desired. Serve immediately.