Wash and skin the eels. Cut into pieces about 3 in. long. Put into a saucepan, add the stock, wine, finely-chopped onion, cloves, lemon rind and seasoning. Simmer gently for ½ hr., or until tender, then lift carefully on to a hot dish. Meanwhile knead together the butter and flour, add it to the stock in small portions, stir until smoothly mixed with the stock. Boil for 10 min., then add the cream and lemon juice and a little more hot stock if the sauce is too thick. Season and strain over the fish.