Cook the Pasta: Begin by filling a large pot with water and bringing it to a rolling boil. Generously add salt to the water, then carefully add the fettuccine. Cook according to the package instructions until the pasta is al dente. Once done, drain the pasta, but reserve about 1 cup of the pasta water for later use. Set the drained pasta aside.
Prepare the Sauce Base: While your pasta is cooking, heat a large skillet over medium heat. Add the unsalted butter and allow it to melt completely. Once melted, add the finely minced garlic and sauté for about 1 minute, stirring frequently, until the garlic is fragrant but not browned.
Incorporate Pumpkin and Cream: Once the garlic is aromatic, add the pure pumpkin puree directly into the skillet. Stir it well to combine with the garlic. Gradually pour in the heavy cream, stirring continuously to ensure the mixture is smooth and well combined.
Season and Create Creaminess: As the pumpkin and cream mixture begins to warm, stir in the grated Parmesan cheese, dried sage, grated nutmeg, and a pinch of salt and pepper. Keep stirring until the cheese melts and the sauce becomes creamy. If the sauce is too thick, gradually add some of the reserved pasta water until you achieve your desired consistency.
Combine the Pasta with the Sauce: Add the drained fettuccine directly into the skillet with the pumpkin Alfredo sauce. Using tongs or a spatula, gently toss the pasta in the sauce until every strand is evenly coated. If necessary, add a bit more reserved pasta water to help the sauce adhere to the fettuccine.
Garnish and Serve: Transfer the creamy pumpkin Alfredo pasta to serving plates or a large serving dish. Garnish generously with freshly chopped parsley and an extra sprinkle of Parmesan cheese. Serve immediately and enjoy.