2) Meanwhile, melt the butter in a large pan. Sweat the onions and celery until soft, about 10 minutes, then stir in the flour and cook until it resembles a paste. Gradually whisk in the chicken stock. Cook until thickened. Add the sweetcorn and cook until heated through.
3) Combine the corn mixture with the bread and milk mixture. Pour into a greased 33cm by 23cm dish. Bake for 45 minutes.