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.