Remove the fillets from the turbots. Skin the fillets. Soak the fillets in cold water. Make the stock: heat the oil in a large flameproof casserole or Dutch oven and add the onion, shallots, garlic, leek, celery and fish bones and heads. Pour in the wine and two cups of water. Season with salt and pepper. Bring to a boil, and place them in a large frying pan. Fill with fish stock to cover. Bring to a boil, reduce heat and simmer for 5 minutes. Drain the fish and place them in a buttered roasting pan. Boil the fish cooking juice very hard until reduced to a syrupy consistency. Stir in the crÅme fraöche and boil until thickened. Season with salt and a pinch of Cayenne pepper. Squeeze the lemon and add the juice to the sauce. Cut the sorrel thinly with a pair of scissors. Melt a little butter in a frying pan and cook the sorrel over low heat. Transfer the sorrel to the sauce with a slotted spoon. Pour the sauce over the fish fillets and bake in the oven for 10 minutes.
