Rémoulade is a mayonnaise-like sauce made with egg yolks, olive oil, garlic tarragon and chervil used to season certain raw vegetables (most often grated celeriac or céleri rave, so often in fact that the salad is practically synonymous with the sauce).
It’s also used (without the celeriac) with meats or fish. Sometimes hard boiled eggs, gherkins, capers and/or anchovies are added.
Rémoulade comes from rémoula, an obsolete word for black radish in Picardy. First mentioned in the 17th century, it seems to predate mayonnaise, leading some food historians to think that mayo was derived from rémoulade.
Image by Alupus