In a large pot of salted boiling water, cook the fettuccine according to package instructions until al dente, about 8-10 minutes. Reserve 1 cup of pasta water before draining the pasta.
In the same pot, heat the olive oil over medium heat. Add the minced garlic and sauté for 1-2 minutes, until fragrant but not browned.
Stir in the pumpkin puree, heavy cream, sage, nutmeg, salt, and pepper. Bring to a gentle simmer, cooking for about 3-5 minutes until slightly thickened.
Add the cooked fettuccine to the pumpkin sauce, tossing to coat evenly. Adjust consistency with reserved pasta water as necessary.
Stir in the grated Parmesan cheese until melted and incorporated. Adjust seasoning with more salt and pepper if necessary.
Plate the creamy pumpkin alfredo pasta, garnishing with extra Parmesan cheese, cracked black pepper, and fresh sage leaves.