Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 9x13 inch baking dish.
Place a steamer basket in a pot over boiling water, and steam the broccoli about 5 minutes, until tender. Place the onions in a separate pot with enough water to cover. Bring to a boil, and cook until tender. Arrange the broccoli and onions in the prepared dish.
Melt the butter in a saucepan over medium heat, and stir in the flour until smooth. Blend in the milk until thickened. Blend in the cream cheese until melted. Pour the mixture over the broccoli and onions. Sprinkle with Cheddar cheese, and top with bread crumbs.
Bake covered in the preheated oven 30 minutes. Remove cover, and continue baking 30 minutes, until lightly browned.
