Peel, seed and cut squash into 1 1/2-inch cubes. Cook in a large saucepan of lightly salted boiling water until tender, about 15 minutes. Drain and let cool. Puree in a food processor. Cover and refrigerate for up to 3 days or freeze for up to 6 months. A 2-pound acorn, buttercup or butternut squash will yield approximately 2 cups puree.