Start by cooking the pasta. Reserve about 1/4 cup of the pasta water to add to sauce if you need to thin it. Drain, don't rinse, set aside.
I the pasta pot, heat back to medium/low heat. Melt the butter. Then whisk in the flour until there are no clumps. Whisk in the coconut milk. It will start to bubble and then you whisk in the seasoning and nutritional yeast. Let sauce thicken. Taste and adjust seasoining like salt and nutritional yeast if needed.