Soften the cashews (optional): If you have a high-powered blender, you can skip this step. Otherwise, add the cashews to a small pot, cover with water, and bring to a boil. Boil for 10 minutes until very tender. Drain and rinse well before using. Alternatively, soak cashews in cool water overnight, drain and rinse before using. (Softening the cashews helps them blend smoothly into a creamy sauce).
Cook the pasta: Bring a large pot of water to a boil. Cook pasta according to package directions until al dente. Drain and set aside.
Make the sauce: Add the cashews, pumpkin, water, nutritional yeast, cornstarch, miso, paprika, salt, garlic powder, onion powder, and black pepper to a blender. Blend until completely smooth, and creamy, stopping to scrape down the sides as needed. (The mixture will be thin but will thicken when cooked).
Thicken the sauce: Return the empty pasta pot to the stove over medium heat. Pour in the sauce and cook, stirring often, until thickened and smooth 5-8 minutes.
Combine: Add the cooked pasta to the pot and stir to coat evenly. If enjoying right away, heat through and serve! Add an extra splash of water or plant-based milk to loosen if needed. Serve as-is, or continue to the next steps for a baked version.