Don’t use pre-grated cheese—it has anti-clumping preservatives that can prevent it from melting well and will make it grainy. Plus, it’s less cost effective. My mac and cheese actually has French roots—the base of the sauce is a béchamel, one of the five French mother sauces, which becomes a mornay sauce when I add grated cheese and seasonings. I always make my mac and cheese a day in advance for the holidays.