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Prince of Wales' Sauce
(For Fish.) Cook a handful of burnet, chervil, and parsley and tarragon leaves, in boiling water for five minutes. Drain and chop very fine, with 2 boned anchovies, yolks of 2 hard-boiled eggs, a pinch of mustard, and the yolk of a raw egg. Pound these to a paste, and add 1/4 pint of pure olive oil and a tablespoonful of lemon juice. Strain for use.
A cold green sauce in the sauce verte family, thickened by the same emulsion that makes mayonnaise. The one thing that decides whether it works is how the oil goes in.
- Add the oil slowlyThe raw yolk, helped a little by the pinch of mustard, is what binds this; the pounded herbs and hard yolks contribute very little. Work the oil in a few drops at a time until the paste thickens and takes a sheen, then in a thin stream; poured in at once it can slide apart into a green oil slick.
- How much is a quarter pintAmbiguous. In an Imperial measure it is 5 fl oz (about 2/3 cup); in a US pint it is 4 fl oz (1/2 cup). Either works, but start at the lower figure and stop when the sauce is the consistency you want rather than measuring to the last spoonful.
- BurnetSalad burnet, a soft-leaved herb tasting faintly of cucumber, once common in kitchen gardens and now rarely sold. Watercress or a little cucumber peel gives a comparable cool note; the sauce is not spoiled by leaving it out, since chervil, parsley and tarragon carry it.
- Blanching the herbsFive minutes is longer than modern practice, which favours thirty seconds to a minute followed by a plunge into iced water. The original is aiming at a soft paste rather than bright colour; blanch briefly and refresh if you want the sauce to stay green rather than olive.
- Squeeze the herbs dry"Drain" is doing a lot of work. Water left in the leaves will thin the sauce and make it break. Wring the blanched herbs in a cloth before chopping.
- Boned anchoviesTwo salt-packed anchovies, rinsed and filleted off the bone, which gives four fillets. Four canned fillets in oil, patted dry, are the nearest substitute; salt levels vary a good deal between brands, so taste before adding any.
- Raw yolkThe sauce is never heated after the yolk goes in. Use a pasteurised egg, or the freshest you can get, and keep the sauce refrigerated and eat it the day it is made.
- StrainingPush the finished sauce through a fine sieve with the back of a ladle. This is what turns a coarse chopped mixture into a smooth sauce, and it is worth the trouble.
- YieldRoughly three-quarters of a cup, enough to serve six to eight alongside cold salmon, turbot or any poached white fish.
Green herb sauces bound with egg and oil run back through French cookery as sauce verte and its cousin ravigote, and this is a Victorian dining-room version of the same idea: herbs blanched to sweetness, anchovy for depth, hard yolks for body, raw yolk to bind. The name follows a nineteenth-century convention of attaching royal titles to hotel and restaurant dishes; during the long decades when Edward VII was Prince of Wales and a conspicuous diner-out, a great many sauces, soups and garnishes acquired his style, often said to be a chef's compliment rather than any documented connection to the man. Salad burnet at the head of the herb list may place the recipe in its period as much as the title does. It was a standard kitchen-garden plant in Britain and is generally thought to have faded from commercial sale over the following century, so a sauce that once began with a handful from the border now begins with a substitution.