Infuse the butter: Melt butter in a skillet, add sage leaves and thyme sprigs, and cook for 30–60 seconds until fragrant. Remove herbs.
Sauté the garlic and pumpkin: Add chopped garlic and pumpkin purée. Cook for 2–3 minutes, stirring often, until slightly thickened.
Season with spices: Stir in onion powder, paprika, chipotle chili powder, and bouillon paste. Cook for another minute.
Add creaminess: Pour in heavy cream and mascarpone. Stir until smooth. Add your pasta water.
Melt the cheese: Reduce the heat to low, and slowly stir in the cheddar, Monterey Jack, and nutritional yeast until the sauce is emulsified and glossy.
Finish with pasta: Add cooked pasta directly into the sauce, tossing with the remaining pasta water. Serve hot.
Notes
Store in the fridge for up to 3 days; reheat with a splash of milk.You can freeze the sauce (but not the pasta) for up to 2 months.Swap mascarpone for cream cheese, or use Gruyère instead of cheddar!Always use pure pumpkin purée, not pie filling.