Cut up onion and fry it in butter, add Burgundy, some cuttings of mushrooms and truffles, parsley and bay leaf. Reduce half.
In another saucepan put Espagnole sauce, veal stock, and essence of fish, reduce one-third and add it to the other saucepan, skim off all the grease, boil for a few minutes, and pass through a sieve. Then stir it over the fire, and add crayfish and anchovy butter.