In a large deep skillet, heat 1 tablespoon of olive oil over medium-high heat. Add onion and garlic and saute until soft, 3-5 minutes. Add pureed butternut squash. Stir in the Parmesan cheese. Season with nutmeg, salt, and pepper. Add the pasta and stir until pasta is well coated. Chop two of the sage leaves and stir them into the pasta. Serve the pasta with remaining fried sage leaves and additional Parmesan cheese, if desired.