All ingredients ready? Let's begin!
Preheat the oven to 350°F. Lightly coat a 9x13-inch pan with butter or spray with cooking spray and set aside.
Cook macaroni in salted water according to package instructions. Drain, and stir 2 tablespoons of butter into the macaroni until melted.
While the pasta is boiling, shred the cheese blocks into a large bowl, combine evenly, and set about half of the mixture aside for later.
In a large bowl, whisk the cream cheese, then whisk in evaporated milk until as smooth as possible.
Mix in the whole milk, the salt, creole or Cajun seasoning, mustard powder, and nutmeg. Stir in half of the shredded cheese mixture until combined. Taste the mixture and season to your preference if needed. Then stir in the beaten egg. Add buttered macaroni and stir to combine.
Pour the unbaked mac-n-cheese into the prepared baking pan.
Sprinkle remaining shredded cheese on top, and sprinkle some freshly ground pepper or more Cajun seasoning. Bake in preheated oven for 50 minutes or until the cheese on top is melted and browned, and the filling is bubbling. Let cool for 10 minutes before serving and dig in!