Heat olive oil in a large pan over medium heat. Add onion and cook for 3–5 minutes, until soft. Add garlic and cook for 1 minute, stirring often.
Stir in pumpkin puree, tomato paste, nutritional yeast, sage, Italian seasoning, nutmeg, salt, black pepper, and red pepper flakes if using. Cook for 1–2 minutes to deepen the flavor.
Slowly pour in vegetable broth, then add plant milk. Stir until the sauce looks smooth and creamy.
Add dried pasta directly to the pan and stir to coat. Bring to a gentle boil, then simmer uncovered for 15–20 minutes, stirring often.
When the pasta is al dente, taste the sauce. Add more salt for flavor, lemon juice or vinegar for brightness, or plant milk if the sauce is too thick.
Spoon into bowls and top with vegan parmesan, black pepper, crispy sage, or pumpkin seeds. Serve while the sauce is warm and creamy.
