Preheat oven to 350. Cut off tips of squash then cut into 3-4 pieces. Drop squash into large saucepan with enough water to cover. Bring to a boil, reduce heat and cook until tender. Drain well.
Butter a 9 x 9 pan well. Set aside. In large bowl mash squash. Stir in egg, crumbs, butter, sugar, onion and salt and pepper. Mix well. Pour mixture into prepared pan. Sprinkle top with additional bread crumbs, if desired. I like cheddar cheese, too.