Cook the pasta: Cook the pasta in a large pot of salted boiling water according to package instructions until al dente. Drain the pasta, reserving 1/2 cup of pasta water. Set the pasta aside.

1. Sauté the onion and garlic: While the pasta is cooking, heat olive oil in a large skillet over medium heat. Add the chopped onion and sauté for about 3-4 minutes until softened. Add the minced garlic and cook for an additional 30 seconds until fragrant.
2. Prepare the pumpkin sauce: Stir in the pumpkin puree, vegetable broth, and heavy cream into the skillet. Add the nutmeg, cinnamon, salt, and pepper, and stir to combine. Bring the mixture to a gentle simmer and cook for about 5-7 minutes, allowing the sauce to thicken slightly. If the sauce gets too thick, add a bit of reserved pasta water to loosen it up.
3. Crispy sage: While the sauce is simmering, heat butter in a separate small pan over medium heat. Once the butter is melted and bubbly, add the sage leaves and cook for 1-2 minutes until crispy. Remove from the heat and set aside.
4. Combine pasta and sauce: Add the drained pasta to the pumpkin sauce and toss to coat evenly. If the sauce is too thick, add a bit more pasta water until you reach your desired consistency.
5. Serve: Divide the pasta into bowls and garnish with crispy sage leaves, grated Parmesan cheese (if using), and a drizzle of olive oil.