Preheat oven to 300°.
With electric knife cut squash in half lengthwise.
Scoop out seeds and fibers.
Place, cut side down, in baking pan with 1/4 inch water.
Bake 1 hour.
Turn squash right side up and sprinkle with brown sugar; dot with butter or margarine.
Continue baking 30 minutes longer or until fork-tender.