To most practising cooks this soup is simply a brown stock flavoured with tomato and strongly flavoured with celery and mushrooms and which is finally finished with the addition of an infusion of turtle herbs.
Carême called this soup Tortue à la Française and posed the following principles:
that the liquid base should be the thinned cooking liquor from a calf’s head,
that the thickening element should be supplied by adding Espagnole in the proportion of 2½ dl (9 fl oz or 1⅛ U.S. cups) per 1 litre (1¾ pt or 4½ U.S. cups) of liquid,
that the flavouring should be celery, mushroom, parsley, thyme and bayleaf, and
that the special flavouring should be that of basil, rosemary and marjoram—these being used in very small quantities of not more than 2 g (1/15 oz) per litre (1¾ pt or 4½ U.S. cups) of soup.
The method of Suzanne who was the popularizer of English recipes is almost the same—the only difference being that he indicates the use of Roux plus arrowroot as the thickening ingredients.
Whichever the preparation, however, the soup is always finished with 1 dl (2 fl oz or ¼ U.S. cup) Madeira per 1 litre of soup and is fairly well seasoned with Cayenne. The garnish is composed of round pieces of cooked calf’s head cut out with a 1½ cm (⅗ in) cutter and small Quenelles made from a mixture of a purée of hard-boiled egg yolks mixed with the required amount of ordinary forcemeat and then moulded with teaspoons.