Chop together very finely the yolks of two eggs, half a dozen gherkins, some capers, a few shallots, and a sheep’s or calf’s brain. Prepare in a basin your oil, vinegar, salt, pepper and mustard. Mix the whole thing and beat it well for some time. This sauce should be quite smooth in appearance and the consistency of thick cream. It is specially good served with hot calf’s head.