Scoop out squash seeds and fibers. Place in a buttered dish and put 1 tsp. each of sherry. brown sugar and butter in each half. Cover and bake in a hot oven 400F for 30 minutes or until tender. Scoop cooked squash out of shells, leaving a wall 1/4" thick. Mash squash and combine with4 tbsp. butter and remaining ingredients, beating well until blended. Spoon back into shells and return to a hot oven 425F for 15 minutes. Serves 6.