Clean and pick over the oysters, reserving their liquor. Cut the firm part of the oysters from the soft part, and chop separately. Simmer the stock with the breadcrumbs, onion, celery, parsley, bay leaf, and firm part of the oysters for 3 minutes. Then remove the leaves, and puree, Melt the butter, stir in the flour, then add the puree and the oyster liquor. Bring to the boil, and add milk, the chopped soft part of the oysters, salt and pepper, and heat. Pur&ecute;e the soup again, or not, as you wish. Serve garnished with chopped fresh parsley or dill and salted whipped cream. Pass crisp oyster crackers with this delicate soup.