It may be helpful to make the squash puree in advance. To prepare the squash puree, cut squash in half lengthwise, scoop out seeds and place cut side down on a buttered baking sheet. Bake at 375F until a fork pierces the shell easily. Time will vary depending on the squash, but roughly 45 minutes. When squash is cool enough to handle, scoop out the flesh and puree in a blender.