This baked yellow squash casserole is topped with a buttery bread crumb topping for a delicious savory addition to any summer meal.
Gather all ingredients.
Preheat the oven to 375 degrees F (190 degrees C). Grease a 2-quart baking dish.
Place squash into a large saucepan, cover with water, and bring to a boil. Boil until soft, 10 to 15 minutes.
Drain squash well, transfer to a large mixing bowl, and mash until slightly chunky.
Stir in 1/2 cup bread crumbs, onion, eggs, 1/4 cup melted butter, sugar, salt, and pepper until thoroughly combined.
Spread mixture into the prepared baking dish. Drizzle remaining 1/4 cup melted butter over top, then sprinkle with remaining 1/4 cup bread crumbs.
Bake in the preheated oven until cooked through and golden brown on top, about 1 hour.