Cook spaghetti according to package instructions. Reserve the pasta water after draining. Set aside.
Heat olive oil in a large pan over medium heat. Once hot, add the flour and nutritional yeast. Cook until golden, stirring frequently, about 1-2 minutes.
Slowly pour in the non-dairy milk while whisking to prevent clumping. Add in the pumpkin and ½ cup pasta water, whisking to combine. Add salt, sage, garlic powder, black pepper, ginger and nutmeg.
Bring to a rapid simmer over medium heat. Once simmering, reduce to a low simmer over medium-low. Just a few bubbles should be popping at a time.
Simmer until sauce is thick and creamy, about 3-5 minutes.
Stir in the cooked spaghetti. If needed, add additional pasta water to thin the sauce. Taste for seasonings and enjoy.
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Notes
Milk: I use soy milk but oat, almond, etc. also work. Make sure to choose unsweetened, unflavored milk for neutral flavor.
Leftovers: Best within 3-4 days. Keep refrigerated in a closed container.
Reheating: You can reheat a serving of pasta in the microwave in just about 2 minutes. Reheat on the stove over medium heat with a splash or two of non-dairy milk to thin the sauce.