01 - Bring a large pot of salted water to a boil. Cook fettuccine or tagliatelle according to package directions until al dente. Reserve 1/2 cup pasta water, then drain using a colander.
02 - While pasta cooks, heat olive oil in a small skillet over medium heat. Add chopped walnuts and toast, stirring frequently, for 3 to 4 minutes until golden and aromatic. Set aside.
03 - In a large skillet, melt unsalted butter with olive oil over medium heat. Add minced garlic and chopped sage; sauté for 1 to 2 minutes until fragrant.
04 - Stir in pumpkin puree, heavy cream, grated nutmeg, salt, and pepper. Simmer gently for 3 to 4 minutes, stirring occasionally until combined.
05 - Add grated Parmesan cheese to the sauce; stir until fully melted and smooth. If mixture is too thick, mix in a small amount of reserved pasta water to reach desired consistency.
06 - Add drained pasta directly to the sauce. Toss thoroughly to coat with pumpkin mixture. Cook for 1 to 2 minutes until fully heated through.
07 - Portion pasta onto plates. Top with toasted walnuts, additional Parmesan cheese, and fresh sage leaves, if desired. Serve immediately.