Bring a large pot of salted water to a boil. Add the pasta and cook 5-6 minutes. Just before draining, remove 1 1/2 cups of the pasta cooking water. Drain. Preheat the oven to 400 degrees F.Heat a large, oven safe skillet over medium heat. Add the sausage, if using, and brown all over, 5 minutes. Remove from the skillet and set aside. Reduce the heat a bit to medium low-ish.Add the olive oil, butter, butternut squash, shallots, garlic, thyme, sage, cinnamon, nutmeg, and season with salt, pepper, and chili flakes. Cook 10-15 minutes, stirring occasionally until the squash softens. Use the back of your spatula or a potato masher to mash the squash down into a chunky puree.Stir in the milk and vodka, cook 5, until you no longer smell the vodka. Add 1/2 cup pasta cooking water, and the parmesan. If needed, thin the sauce with additional pasta cooking water. Remove from the heat. Mix in the pasta, sausage, and 1/2 cup of cheese. Scatter the remaining cheese on top, then drape the prosciutto over the cheese. Bake 15 minutes or until the cheese is bubbling. Top with fresh herbs, and enjoy!