Peel and cube the butternut squash.
Add the squash, heavy cream, butter and 3⁄4 cup of water to a large saucepan and bring to a boil.
Reduce the heat to a simmer and let the squash cook until it's tender enough to be mashed with a fork.
Add the mixture to a blender or use an immersion blender to puree until creamy and smooth.
Add the nutmeg and kosher salt.
In the meantime, prepare the fettuccine according to the package directions.
Before straining, reserve about 3⁄4 cup of the pasta water.
Add the strained pasta and parmesan to the pureed squash mixture and stir until well coated.
If the sauce is too thick for your liking, add the reserved pasta water 1 tablespoon at a time.
Sprinkle a little extra nutmeg, parmesan, and parsley on pasta before serving.