01 - Bring a large pot of salted water to a boil. Cook the pasta until al dente according to package instructions. Reserve 1/2 cup of pasta water, then drain the pasta.
02 - Heat olive oil in a large skillet over medium heat. Add the chopped onion and cook until translucent, about 3 to 4 minutes. Add minced garlic and sauté for 1 minute until fragrant.
03 - Stir in pumpkin purée, vegetable broth, heavy cream, ground nutmeg, salt, and black pepper. Simmer the mixture for 5 minutes, stirring occasionally to blend flavors.
04 - Add the drained pasta to the sauce and toss to coat evenly. If the sauce appears too thick, gradually add reserved pasta water until the preferred consistency is achieved.
05 - Stir in the grated Parmesan cheese until fully melted and integrated. Taste and modify salt and pepper as needed.
06 - Plate the pasta immediately, garnishing with additional Parmesan and chopped fresh sage leaves if desired.