Bring a large pot of salted water to a rolling boil. Add the penne pasta and cook according to package directions until al dente. Before draining, scoop out and reserve 1 cup of the starchy pasta water. Drain the pasta and set aside.

While the pasta cooks, heat the olive oil in a large skillet or Dutch oven over medium heat. Add the finely diced yellow onion and sauté for 5-7 minutes, until it softens and becomes translucent.

Add the minced garlic and finely chopped fresh sage to the skillet. Cook for another 1-2 minutes until fragrant, stirring constantly to prevent the garlic from burning.

Stir in the canned pumpkin puree, vegetable broth, and ground nutmeg. Bring the mixture to a gentle simmer, then reduce the heat to low and let it cook for 5 minutes, allowing the flavors to meld.

Pour in the heavy cream and stir until well combined. Gradually add the 1/2 cup of grated Parmesan cheese, stirring continuously until the cheese has melted and the sauce is smooth and creamy. Season generously with salt and freshly ground black pepper to taste.

Add the drained pasta directly to the skillet with the pumpkin sauce. Toss gently to coat all the pasta evenly. If the sauce appears too thick, add a splash or two of the reserved pasta water until it reaches your desired silky consistency.

Serve the Creamy Pumpkin Sage Pasta immediately, garnished with extra grated Parmesan cheese, a few fresh sage leaves, and a sprinkle of crushed red pepper flakes for a subtle kick, if desired.