Preheat the oven to 400ºF. In a large bowl, combine half of the squash with a drizzle of olive oil. Season the the fresh nutmeg, salt and pepper. Spread on a baking sheet and roast until the squash is tender, about 20 minutes.

Meanwhile, combine the remaining squash, the chicken stock, onion, bay leaf, garlic and salt to taste in a medium saucepan. Bring the mixture to a simmer and cook until the squash is tender, about 15-20 minutes. Remove the onion and bay leaf and puree the mixture with an immersion blender or transfer to a blender and process until smooth. The mixture will be loose, and should coat the back of a spoon.

Bring a large pot of salted water to a boil, then add the pasta and cook according to the package directions.

Place a small skillet over medium heat and add the butter. Once the butter melts and the foam subsides, add half of the sage leaves and fry until crisp. Remove to a paper towel, and fry the remaining leaves. After removing the leaves from the butter, pour the butter into the squash puree and stir to combine.

Heat a large skillet over medium-high heat. Heat the olive oil, then add the sausage and cook, breaking it up with wooden spoon as it cooks. Cook until the sausage is browned and cooked through.

Reserve a mugful of the pasta water, then drain the pasta. Return the pasta to the pan, then add the squash puree and the sausage. If needed, add some of the pasta water to loosen the sauce. Stir in the creme fraiche, then toss the pasta with the sauce for a minute or two so the flavors will be absorbed. Stir in the roasted squash.

Serve the pasta topped with the crispy sage leaves and grated Parmesan cheese.