French Salsa Verde / Sauce Verte
What it is
In classic French cuisine, sauce verte ("green sauce") is most precisely a green mayonnaise — a cold emulsified sauce of mayonnaise tinted and flavored with a purée of blanched green herbs and leaves (commonly spinach or watercress for color plus tarragon, chervil, parsley, and chives) — served with cold fish, shellfish, and cold poultry. This is worth stating plainly because the French "green sauce" is built on a fundamentally different structure from its Italian and Argentine namesakes: it is an egg-emulsified sauce, not an oil-suspension or vinaigrette. (France also has rustic regional herb-and-oil green sauces, but the canonical sauce verte of the classic repertoire is the herb mayonnaise.)
The science
Where Italian salsa verde is a loose suspension and chimichurri a broken emulsion, French sauce verte is a stable emulsion: egg yolk lecithin and proteins coat dispersed oil droplets so they stay permanently suspended in the water phase, giving the thick, glossy, spoon-coating body of mayonnaise. The herbs are blanched briefly and shocked in ice water before being puréed and squeezed dry — blanching deactivates the browning enzymes (as with basil) to fix a brilliant green, sets the chlorophyll, and removes harshness, while squeezing out water keeps the mayonnaise from thinning and breaking. Watercress or spinach is included mainly as a color and body vehicle; tarragon and chervil supply the defining anise-herb perfume.
How it's made
Make (or start from) a firm mayonnaise. Blanch the herb leaves a few seconds, shock in ice water, squeeze very dry, and pound or blend to a fine paste, possibly with a little of the mayonnaise to loosen. Fold the herb purée into the mayonnaise, season, and adjust acid with lemon. Keep cold. It is never heated.
Regional variations
Sauce verte is part of the codified grande cuisine repertoire (it appears among the cold mayonnaise derivatives in Escoffier-era classifications). Beyond it, French regional cooking has its own green herb-and-oil sauces and vinaigrettes, and the broader European family includes the German Frankfurter grüne Soße (a cold sauce of seven herbs in a sour-cream or yogurt base) — another reminder that "green sauce" is a category, not a recipe.
Cultural & historical context
The herb-mayonnaise sauce verte belongs to the cold-buffet and garde-manger tradition of classic French restaurant cooking, where cold poached fish and elaborate cold presentations demanded vivid, stable, flavorful cold sauces. Its codification is part of the 19th–20th-century French systematization of sauces into mother sauces and their derivatives.
Reference notes
Cross-link to: mayonnaise (its base), Italian salsa verde and Mexican salsa verde (same-name contrast), the technique of blanch-and-shock for color fixation (shared with the basil/PPO discussion in pesto), cold garde-manger sauces, Frankfurter grüne Soße. The clearest example in this complex of how structure (emulsion vs. suspension) — not just ingredients — distinguishes "green sauces."
When to use
As a cold sauce for cold protein: poached salmon and other cold fish, shellfish, cold chicken, hard-boiled eggs, and crudités. Choose it when you want richness and herbal freshness in a single cold sauce — the creaminess that the Italian and Argentine green sauces deliberately avoid.
What goes wrong
Breaking the mayonnaise (oil added too fast, temperature shock, or too much watery herb purée). Dull grey-green color from un-blanched or over-blanched herbs. A thin, weeping sauce from herb purée that wasn't squeezed dry. Bitterness from too much watercress.