In a large pot of boiling salted water, cook the pasta al dente according to package instructions. Reserve 1 cup pasta water, drain and set aside.
Heat the olive oil in a large skillet over medium heat. Add the garlic and sage, and cook until aromatic, 1 minute. Add the pumpkin puree, salt, pepper and nutmeg and continue to cook for 2-3 more minutes. Add the milk and stir until well combined and creamy.
Toss the reserved cooked pasta with the sauce, add ½ cup of the reserved pasta water to combine until the sauce clings to the pasta and is glossy.
Sprinkle the grated parmesan cheese on top, if using and serve immediately.
Notes
Storage: Store any leftovers in an airtight container. They will last about 4-5 days in the fridge.