Hey, I make mine almost the same way I did as a vegetarian, make a basic roux with vegan butter or olive oil with plain flour, combine over heat and stir til it makes a paste, cook it down a little then whisk in plant milk of choice, cook down further - very slowing adding a little more flour or milk as required for your preferred consistency. Then add a heap of nooch, some nutmeg, salt and pepper to taste. Ta-daa! Also you can add your fave plant cheese if you want it extra cheesy. I use this sauce for cauliflower or for pasta.

I'm a little late to the vegan mac and cheese discussion but here is my recipe: boil 2 small white potatoes, 1 carrot, and half a small onion all quartered in 4 cups water until tender. Blend. That's your 'cheese' sauce. You can add unhealthy things to it to make it more like mac and cheese such as vegan margarine, salt, a handful of raw cashews for a creamy texture, nooch, and I love to add a squeeze of fresh lemon. It gives the flavor a sharp edge. If I'm making it for my family they like me to top it with canned french fried onions. 1/8th of the pan is 475 calories for the full fat, onion topped version.

Just make sure you bake it in a casserole dish until bubbly and if onion topped, browned.

This is my kids favourite!
https://veganyumminess.com/creamy-vegan-mac-and-cheese/