Wash and peel squash; trim ends. With a sharp chef’s knife, cut bottom third off of the squash, then halve that and scrape out the seeds with a spoon. Chop the entire squash into roughly 1-1/2 inch pieces.
Place squash in a medium pot and fill with cold water. Add a 1/2 teaspoon of salt and place over high heat. Cover pot, bring to a boil, then reduce heat and simmer until squash is tender; about 10 minutes.
Drain, return the squash to the pot and mash with a potato masher or whirl with an immersion blender.
Puree can be made up to one day in advance and refrigerated in an airtight container.