Wash and scrub the mussels to get rid of sand or grit, discarding all that are open. Then put them into a large saucepan with the cider. Cover and bring to the boil, then cook for about 5 minutes, shaking the pan, until they are all open. Leave to cool a little, then strain but reserve the liquor. When cool enough, take the mussels from their shells and remove the beards.

Heat the butter, add the flour and let it cook for a minute, then gradually add the mussel stock, stirring until it boils and is smooth and creamy. Add the finely chopped celery and onion to the thickened stock and cook until they are quite tender.

Taste for seasoning, add the cream and finally the mussels. Heat gently but do not allow to reboil. Serve with a garnish of parsley.