Cut open the winter squash and remove seeds. Place in a baking dish and bake in a 400? oven or toaster oven until very soft, about 40 minutes. When the squash is almost ready, cut the potatoes into chunks and simmer until soft, 10-15 minutes. Drain, reserving water for future soup stock.
When the squash is soft, remove from the oven, and remove peel if necessary. Place the squash in with the potatoes, add the butter and mash together, until blended, leaving a few small chunks of both potato and squash for texture. If too dry, blend in a little of the potato water. Add salt and pepper to taste and serve.