This recipe uses a nutritional yeast-based cheeze sauce. You can find the recipe in Vegan Vittles by Jo Stepaniak. I highly recommend Vegan Vittles.
The sauce has to be tended to the whole time you’re cooking it. While the macaroni is cooking, you’ll be whisking small amounts at a time of warm soymilk into the nutritional yeast/flour/spices base. After you drain the macaroni, you mix it with the sauce and then bake it for 25 minutes.
Shop Natural, an online store, sells Red Star Nutritional Yeast in 16 oz. packages. They also have larger bulk bags. Be sure to sign up for their monthly email newsletter. Each newsletter has a discount coupon code.