Preheat the oven to 400 degrees.
2
Cut off and discard the ends of the squash. Peel the squash, cut them in half lengthwise, and remove the seeds. Cut the squash into 3/4 inch cubes and place them on a baking sheet. Add the melted butter, brown sugar, salt and pepper. Toss all the ingredients together and spread in a single layer. Roast for 30 minutes, or until the squash is very tender. While roasting, turn the squash once to be sure that it cooks evenly. Do not let it brown.
3
Transfer the squash and the pan juices to a large mixing bowl, and mix with an electric mixer until smooth. It should have the consistency of mashed potatoes.