Beurre blanc

In cooking, Beurre blanc—literally translated from French as "white butter"—is a rich, hot butter sauce made with a reduction of vinegar or white wine and shallots into which cold, whole butter is blended off the heat to prevent separation. (Lemon juice is sometimes used in place of vinegar and stock can be added as well). This sauce originates in the Loire Valley cuisine.

It is not uncommon to see recipes that include a beurre blanc sauce to which heavy cream has been added as a "stabilizing agent". This is a point of contention amongst many culinary enthusiasts and can be heavily frowned upon. Chef Anthony Bourdain famously wrote in his novel Bone in the Throat: "There is no, I repeat, no, cream in a real beurre blanc ... You see any mention of cream in there? No ... you put cream in there, it ain't a beurre blanc." To be precise: Adding double (heavy) cream to beurre blanc turns it into beurre nantais (Nantes butter).

Origin
Although contested, the prevailing tale of the creation of this sauce takes us to the kitchens of the Marquis de Goulaine. During the preparation of an important dinner, the head chef asked an assistant to prepare a bearnaise sauce intended for fish, to which the assistant forgot to add the tarragon and egg yolks. Having no time to correct the mistake, the sauce was served as it was, and much to the surprise of the chef, was praised as a wonderful sauce and named beurre blanc.