Preheat oven to 400 degrees. Coat a baking sheet with cooking spray. (I like olive oil cooking spray).
Cut off ends of the squash and discard. Peel squash, cut it in half lengthwise, and remove the seeds. Cut the squash into ¾-inch cubes and place it on a prepared baking sheet. Sprinkle brown sugar evenly over the top of the squash. Spoon melted butter evenly over the top. Sprinkle with salt and pepper. Toss together all ingredients and spread in a single layer.
Place in oven and bake for 40 minutes or until the squash is tender. Using a spatula, turn over squash after 20 minutes.
In a food processor fitted with a metal blade, place cooked squash, pan liquids, and warmed milk. Pulse until squash is coarsely pureed. If you don’t have a food processor, place everything in a medium-size bowl. Using a potato masher or the back of a fork, mash the cubes of squash until pureed.
Serve warm.