To make the Pumpkin Cream Sauce: In a large skillet, heat oil and sauté onions until soft. Add garlic and let cook a few more minutes. Remove from heat. In a blender, puree the onion mixture, pumpkin, tomato paste, milk, nutmeg, and cayenne until smooth.
Pour into a pot and heat. Add generous amounts of salt and pepper. Stir in Parmesan until melted.
Meanwhile, bring a large pot of heavily salted water to a boil. Add penne and cook according to package directions. Drain and return to pot.
To assemble the pasta: Toss hot pasta with Pumpkin Cream Sauce (there might be extra sauce), toasted pecans and fresh sage. Dig in!