Heat oven to 350°F. Spray 13x9-inch (3-quart) glass baking dish or 3-quart casserole with cooking spray.
In 4-quart Dutch oven, melt 1/2 cup butter over medium heat. Add onion; cook 3 to 4 minutes, stirring frequently, until tender. Stir in flour, salt and pepper until well blended. Stir in milk. Cook 4 to 5 minutes, stirring constantly, until thickened. Gradually stir in eggs and cheese. Stir in corn and parsley. Pour into baking dish.
In small bowl, mix bread crumbs and 3 tablespoons melted butter; sprinkle over corn mixture.
Bake uncovered 55 to 65 minutes or until mixture is set and knife inserted in center comes out clean. Let stand 5 to 10 minutes before serving.