Scrub the cockle shells very well under cold running water, discarding any that are already open. Place the cockles in a large saucepan and cover with cold, well-salted water. Bring slowly to the boil, shaking the saucepan from time to time. As soon as the cockles are open they are ready. Do not over-cook as this will toughen them.

Allow the cockles to cool in the stock, then strain, reserving the stock, and remove the cockles from their shells using a sharp knife. Strain the cooled stock again and make up to 900 ml (1 1/2 pints) with water if necessary.

Melt the butter in a saucepan, stir in the flour and cook for 1 minute. Gradually add the cockle stock, stirring to prevent lumps forming. Bring to the boil then stir in the milk. Add the onion and celery and cook, stirring, for 5-10 minutes, or until the vegetables are soft. Add the parsley and pepper, then stir in the cockles.

Heat through thoroughly and pour into 4-6 soup bowls. Swirl a tablespoon of cream into each bowl and garnish with a little parsley. Serve with crusty bread.