Place the butternut squash in a saucepan, cover with water, add ½ teaspoon of salt and bring to a boil. Boil until the squash is very tender, about 15 minutes.

While the squash is cooking, prepare the pasta - bring a large pot of heavily salted water to a boil. Add the pasta and cook according to the directions. Remove about 2 cups of the pasta water, drain the rest and return the pasta to the hot pot.

When the squash is very tender, drain off the water and return the squash to the hot pot. Mash the squash with a potato masher until fairly smooth. Add the nutmeg, rosemary, and garlic and cook over low heat for about 5 minutes to meld the flavors. Stir in the Parmesan or nutritional yeast.

Add the squash mixture to the pasta with about ¾ cup of the reserved pasta water. Stir to combine and add more water, a little at a time, if needed, until the sauce is creamy. Taste and season with salt and pepper.

Serve the pasta topped with some chopped walnuts and dried cranberries.