Bring a large pot of water to a boil. Salt the water heavily.
Add your pasta of choice and cook according to the box instructions until al dente. Make sure to reserve about ½ cup of the starchy pasta water. This will help to adjust the consistency of the pumpkin sauce
Add your non-dairy milk to a large measuring cup or bowl. Use a whisk and combine the pumpkin purée with the milk until fully incorporated. Set to the side.
In a large heavy-bottomed pot or pan, such as a dutch oven, melt the vegan butter over medium heat.
Once butter is fully melted, add the 5 or so large sage leaves. Let them sizzle on medium heat until they begin to curl on the edges. Remove them with a fork and set to the side.
Gently sprinkle the all-purpose flour over the butter and whisk until you form a roux with no clumps.
Continue stirring and allow the roux to cook for about 1 minute.
Then, slowly whisk in the pumpkin and milk mixture.
Whisk to thoroughly combine the milk mixture with the roux. Bring to a simmer until thick.
Once the sauce has thickened, add the nutmeg, cinnamon, garlic powder, nutritional yeast, salt, and pepper.
When the pasta is done cooking, drain and add it directly to the sauce.
Mix thoroughly to combine.
Taste and adjust seasonings and salt levels accordingly. Use the leftover pasta water to make the sauce thinner if you prefer it that way.
Serve hot and garnish with the sizzled sage leaves.