1. Wash and chop the leeks, discarding the tough green leaves, but using as much of the green part as possible; peel and chop the Potato. 2. Cook these very gently in the butter together with the bay leaf, for about 10 minutes, stirring occasionally, but do not let them brown. 3. Add the water and cook gently for about 30 minutes, then sieve or liquidise. 4. Return to the pan, add the cream, parsley and seasoning, but do not let it boil.