Sauce Vénitienne — Tarragon, Chervil, and Shallot Wine Sauce

Sauce vénitienne is a delicate green-tinted fish sauce built on a white wine reduction perfumed with tarragon and chervil, finished with a herb butter that gives it its characteristic pale jade colour. The sauce begins as most fish sauces do: shallots sweated in butter, deglazed with white wine and tarragon vinegar, reduced by two-thirds. Fish velouté is added and simmered for 10 minutes. The defining element is the beurre vert — green herb butter made by blanching tarragon and chervil leaves in boiling water for 10 seconds, shocking in ice water, then pounding in a mortar with softened butter until the mixture is smooth and vividly green. This green butter is whisked into the strained sauce off heat, turning it from ivory to a subtle sage-green that gives the sauce its name and its visual identity. The flavour should be delicate: tarragon's anise note should thread through the sauce without dominating, chervil should contribute its mild, almost parsley-like freshness, and the fish velouté base should carry the seafood character. Sauce vénitienne is the classical accompaniment for poached fish — turbot, sole, salmon — and demonstrates the saucier's ability to build complexity from simplicity. The green must be natural and subtle; if the sauce looks like pesto, the herb butter was too generous.