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Cold Green Sauce for Fish
Take some tarragon, chervil, parsley, and a little shalot. Blanch and pound in a mortar with a little butter, and pass it through a hair-sieve; add a little white sauce made with fish stock, season with pepper, salt and cayenne, then freeze.
A herb butter thinned with fish velouté and then set cold — closer to a savoury frozen butter than to a modern sauce verte. Two words in the original do the most work: blanch and freeze.
- Blanching is the colour stepDrop the picked leaves into boiling salted water for 20-30 seconds, then straight into ice water and squeeze dry. This fixes the chlorophyll so the finished sauce stays green instead of turning olive as it sits.
- "Freeze" means firm, not frozen solid"Freeze" and the ice pail -- In a period kitchen this meant working the sauce in a pail packed with ice and salt; how hard it was taken is not stated. Chilling in the refrigerator until it sets to a spreadable paste is the easiest modern equivalent, and a domestic freezer will probably take it further than is useful.
- ShalotShallot. One small shallot is enough for a batch this size — blanch it with the herbs to take the raw edge off, or the sauce will taste sharp when cold.
- Hair-sieveA fine horsehair drum sieve. Hair was the usual fine sieve material before closely woven wire mesh became common, and was held to be kinder than tinned metal to green herbs and acids. A nylon or stainless fine-mesh sieve, or a tamis, does the job; press with a plastic scraper rather than a wooden spoon for a smoother pass.
- Quantities are left to the cookA workable proportion is about 1 cup loosely packed mixed herbs to 4 oz (115 g) softened butter and 3-4 tablespoons of the fish velouté. Keep the sauce thick — too much liquid and it will not set cold.
- White sauce made with fish stockA velouté: roux cooked without colour, moistened with strained fish fumet, simmered until it coats and thoroughly cooled before it goes near the butter. Warm sauce will split the mixture.
- ChervilRarely stocked and short-lived. Fresh tarragon and parsley carry the sauce on their own; a little dill is a reasonable stand-in for chervil's mild anise note, though not the same thing.
- Serving and yieldAbout 3/4 cup, enough for six as an accompaniment. Intended for cold poached fish — salmon, turbot, trout — quenelles or a fish mayonnaise, spooned or piped alongside rather than poured over.
Cold green sauces for fish run back through the medieval sauce verte of pounded herbs, bread and vinegar, but this version looks like the work of a professional kitchen: the herbs are bound with butter and a fish velouté, and the whole thing is set on ice. Freezing savoury preparations is often said to have been a mark of a well-equipped house, since ice was bought in or cut and stored, and a cook who could turn out an iced sauce, an iced soup or a savoury ice arguably signalled that the establishment had the ice, the pails and the labour to do it. The method assumes a mortar, a hair-sieve, standing fish stock and a freezing pail, and it gives no quantities at all.