Roast the Squash: Preheat the oven to 375°F. Slice the butternut squash in half from stem to bottom and scoop out the seeds. Drizzle a baking dish with olive oil and place the squash cut-side down. Roast for about 20 minutes or until fork-tender. Once cool, peel and puree the flesh in a food processor until smooth.

Cook the Pasta: Bring a large pot of salted water to a boil. Cook the fettuccine until al dente (about 10-12 minutes).

Prepare the Sauce: While the pasta cooks, melt butter in a saucepan over medium heat. Whisk in the flour and cook for 1 minute to create a light roux.

Deglaze and Simmer: Whisk in the sherry until smooth, then add the heavy cream and chicken stock. Stir constantly for 1-2 minutes until the sauce begins to thicken.

Infuse the Sage: Add the fresh sage leaves to the sauce. Cover the pot and reduce heat to the lowest setting, allowing the sage to infuse the cream for several minutes.

Finish the Sauce: Remove and discard the sage leaves. Stir in the 1 cup of butternut squash puree and the Parmesan cheese. Season with salt and pepper. (Note: If the sauce is too thick, add a few tablespoons of the pasta cooking water).

Assemble: Drain the pasta and toss immediately in the warm sauce. Garnish with fresh chopped parsley and serve.