Cook the fettuccine pasta according to package instructions in a large pot of salted boiling water until al dente. Reserve 1/2 cup of the pasta water, then drain the rest and set the pasta aside.
In a large skillet over medium heat, melt the butter. Add minced garlic and sauté for about 1 minute until fragrant, being careful not to burn it.
Stir in the pumpkin puree and heavy cream, mixing well until combined.
Add the grated Parmesan cheese, dried sage, nutmeg, and season with salt and pepper. Stir until the cheese has melted and the sauce is smooth. You can adjust the thickness of the sauce by adding reserved pasta water, a little at a time.
Add the cooked fettuccine to the skillet, tossing until the pasta is well coated with the pumpkin Alfredo sauce.
Continue to cook for 2-3 minutes, ensuring everything is heated through.
Serve hot, garnished with freshly chopped parsley.
Notes
Adjust the thickness of the sauce with reserved pasta water as needed.