Shred your own cheese for the smoothest melt (pre-shredded cheese can be coated to prevent clumping). Making the mac and cheese ahead helps it spread—cool slightly before topping the crust. Store leftovers airtight in the fridge up to 3 days; reheat on a rack in a 350°F (175°C) oven to keep the crust crisp. To freeze, wrap an unbaked assembled pizza tightly in plastic wrap and foil for up to 2 months; bake from frozen, adding a few extra minutes.