Beurre blanc sauce is a rich French sauce made from an acidic reduction whisked together with chunks of fresh butter. The result is used on things like fish, eggs, poultry, and vegetables to add a complex, rich layer of flavor. Many French restaurants offer foods lavishly garnished with beurre blanc sauce, and the food can also be made at home relatively easily, for patient cooks with steady hands.

In French, beurre blanc translates into “white butter.” The name is a reference to the fact that while the sauce is cooked and blended, it is not browned, as in the case of things like roux. Beurre blanc sauce is sometimes mixed with other ingredients, but as a general rule it makes a delicate white sauce, rather than a heavier and more dense brown sauce.

The origins of beurre blanc sauce are largely shrouded in fantasy. One popular tale says that a cook was preparing a complex meal for a head of state, and accidentally left both the egg and the tarragon out of bernaise. Since the cook did not have time to fix the food, it was sent out as is, and to the cook's surprise, the dish was deemed a success. Others suggest that the sauce was developed intentionally, perhaps as a light sauce for mild freshwater fish such as trout.

A traditional beurre blanc sauce starts with reducing very finely chopped shallots in vinegar, lemon juice, or white wine. Once the acidic reduction is made, chunks of slightly softened butter are added and briskly whisked in. Cooks whisk rapidly, to capture multiple small air bubbles in the sauce so that it will hold up well. Beurre blanc sauce is usually used immediately, and cooks differ on whether or not to strain it.

Some cooks add cream to a beurre blanc sauce, to stabilize it. This deviation from traditional should not technically be called beurre blanc sauce, since the cream dramatically changes the composition and texture of the sauce. Other ingredients such as tarragon or dill may be added as well, for additional flavor.

To make a basic beurre blanc sauce, use two thirds of a cup of wine, vinegar, lemon juice, or some combination of these ingredients. Heat it on a medium temperature setting along with two finely chopped shallots until the volume of the liquid has been reduced to approximately one quarter of a cup. Allow the mixture to cool before placing it over low heat and quickly whisking in three quarters to one cup of unsalted butter broken into chunks. Strain, if desired, and add salt and pepper to taste.