In a large pot, bring salted water to a rolling boil. Add 12 ounces of fettuccine and cook according to package instructions until al dente, typically about 8-10 minutes. Stir occasionally to prevent sticking. Once cooked, reserve 1 cup of pasta water, then drain the fettuccine and set it aside while you prepare the sauce.

In a large skillet over medium heat, add 4 ounces of sliced prosciutto. Cook for about 3-5 minutes, flipping occasionally, until the prosciutto is golden brown and crispy. Transfer the crispy slices to a paper towel-lined plate to drain excess fat, leaving the flavorful drippings in the skillet for the sauce.

In the same skillet with the drippings, add 1 diced onion and 2 minced garlic cloves. Sauté over medium heat for 3-4 minutes, stirring frequently, until the onion becomes translucent and fragrant.

Add 1 cup of pumpkin purée and 1 cup of heavy cream to the skillet with the sautéed onions and garlic. Stir well to combine, then season with ½ teaspoon of nutmeg and salt to taste. Let the mixture simmer on low heat for about 5 minutes, until it thickens slightly and becomes creamy.

Carefully add the cooked fettuccine to the pumpkin Alfredo sauce while tossing to ensure the pasta is fully coated. If the sauce is too thick, gradually add the reserved pasta water until you reach your desired creaminess.

Plate the creamy pumpkin Alfredo pasta and generously top with the crispy prosciutto you prepared earlier. Finish with freshly grated Parmesan cheese and optional chopped parsley for a pop of color. Serve immediately while hot.