This sauce, invented by a certain Vincent La Chapelle in the 18th century, is probably a take on the ‘green sauce’ mentioned by Rabelais. These days sauce Vincent is a green mayonnaise, blended with cress, spinach, chervil, tarragon, sorrel, etc and a hard boiled egg. It goes with cold fish dishes and seafood: saumon à la parisienne is the classic dish associated with sauce Vincent.
Beurre de Montpellier is similar, but uses butter and anchovies.
sauce Cambridge is said to be an anglicized version of sauce Vincent, but calls for hard-boiled eggs puréed with oil, capers, anchovies, herbs, a little Cayenne pepper, and vinegar.
Image by Jpbrigand