How to Make It
Preheat oven to 375°F. Cook the pasta according to the package directions. Drain and return the hot pasta to the pot. Add the butter, tossing until melted.
Whisk together the evaporated milk, skim milk, eggs, salt, nutmeg, and cayenne in a medium bowl. In a separate bowl, combine the American cheese, Gruyère, and Cheddar.
Spread ⅓ of the pasta in the bottom of a 9-by-13-inch baking dish. Top with ⅓ of the cheese mixture. Repeat with the remaining pasta and cheese, then pour the milk mixture over the top. Bake until warmed through and golden, 20 to 30 minutes.
How to freeze and reheat: Bake, cool completely, then wrap the dish tightly in plastic wrap and foil and freeze. Defrost before reheating. Remove the plastic wrap and re-cover with the foil, then bake in a 350°F oven for 25 to 30 minutes, until warmed through.