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Green Sauce
Plunge six well-washed, very green leaves spinach in a little boiling water five minutes. Remove, drain on a sieve, and press out water. Then place in a mortar one sound, peeled shallot, one branch parsley, half a branch chervil and six leaves tarragon and pound to a pulp, then add the spinach, pound again till smooth and rub it through a sieve upon a plate. Prepare a mayonnaise dressing add the green puree to the mayonnaise, little by little, continually mixing meanwhile, pour into a saucebowl and serve.
This is the classic sauce verte — a green herb purée folded into mayonnaise. The original assumes you already know how to make the mayonnaise and gives no quantity for it, so the proportions need a decision before you start.
- QuantitiesThe original gives no quantity for the mayonnaise, so this has to be decided. Six spinach leaves plus the herbs will tint and flavour something in the region of a cupful, enough to fill a saucebowl for a cold salmon, chicken or hard-boiled eggs.
- "One branch"A branch is a sprig — a single stem with its leaves, not a whole bunch. Chervil is the one to hunt for; it is faintly aniseed and bruises easily, and flat-leaf parsley plus a little extra tarragon is the usual substitute if none can be had.
- Blanch, then shockFive minutes is longer than spinach needs for colour alone, but it also softens the leaf for pounding. Drop the drained leaves into cold water before pressing them dry and the green will stay bright rather than turning olive.
- Squeeze hardThe single thing that ruins this sauce is water. Press the spinach in a cloth until no more liquid comes, or the mayonnaise will thin and eventually split when the purée goes in.
- Mortar or machineA small blender or spice grinder does the pounding, but it will not give the fine texture the sieve step is there for. Rubbing the purée through a fine sieve is what keeps the sauce smooth rather than flecked; skip it and you have a herb-speckled mayonnaise, which is a different and coarser thing.
- The raw shallotPounded raw shallot is sharp and gets sharper as the sauce sits. Use a small one, and if the sauce will be made more than a couple of hours ahead, consider soaking the chopped shallot in cold water for ten minutes first.
- Raw egg in the mayonnaiseThe mayonnaise base is uncooked egg yolk. Use pasteurised eggs if serving anyone pregnant, elderly, very young or immune-compromised, and keep the finished sauce refrigerated.
- Adding the puréeLittle by little is meant literally — a spoonful at a time, beaten in fully before the next. Dumping the cold purée in at once is the most common way to break an otherwise stable mayonnaise.
Green sauce in this form is French rather than international: sauce verte is generally traced to the cold-kitchen repertoire of the later nineteenth century, though green sauces of other kinds long predate the mayonnaise-based version. It is built on the same logic as rémoulade and sauce tartare — a mother mayonnaise given a character by one addition. The spinach is there chiefly for colour, carrying the green through the sauce in a way the herbs alone cannot, while the flavour comes from the tarragon and chervil, two of the four fines herbes. The instruction to pound in a mortar and then pass through a sieve is a reminder that before the electric blender, smoothness was a matter of labour.