Cut the parboiled and cooled sweetbreads into halves and cover with chaudfroid sauce. Decorate the sauce with bits of truffle and white of hard-boiled egg. When the sauce with decoration is "set," brush or pour over it some liquid aspic jelly and set aside to become thoroughly chilled. Serve with lettuce, celery, cress or tomato salad dressed with mayonnaise. Arrange half a tomato and a slice of sweetbread, alternately, in two rows on a dish with heart leaves of lettuce between. Pass mayonnaise in a separate dish.