*If you wanted to make this mac and cheese gluten-free, I've had good luck making a roux (flour and butter mixture) using sweet rice flour in place of the wheat flour. I suggest using 1 TBSP less of the rice flour, as it can sometimes leave a grainy texture behind. Of course, swap the noodles for your favorite gluten-free variety, too.
A word about leftovers: when the mac and cheese cools, the sauce will thicken up quite a bite. To thin it out, just ad a little extra milk while you re-warm it. I successfully made a whole pot of this in advance, kept it in the fridge, and then reheated it slowly over a medium-low flame, stirring frequently, with about ¼-1/2 cup extra milk added. Be sure to adjust the seasoning after adding any additional milk, as it will dilute the flavor a bit. And, if you actually plan on making this in advance of when you want to serve it, it's a good idea to undercook the noodles a touch, as they will finish cooking while you warm everything back up.
Recipe adapted from my dad's recipe, with some inspiration from this
copycat Panera Mac and Cheese from Food Folks and Fun.