Green Sauce

Wash some parsley leaves, chervil, tarragon, and burnet; plunge them into boiling water in a copper vessel, and blanch them for three minutes; drain, press out all the liquid and then pound the herbs in a small mortar with a few chives added; press them through a sieve, and put into the same mortar a few hard boiled egg-yolks and some anchovy fillets; pound them also, and stir in gradually the green puree; dilute the preparation with some oil, vinegar and mustard, and finish the sauce with a spoonful of finely chopped pickled gherkins.