By Harold McGee
The French sauce beurre blanc probably evolved from the practice of enriching cooking liquids with butter. It’s made by preparing a flavorful reduction of vinegar and/or wine, then whisking pieces of butter into the reduction. Each piece of butter carries all the ingredients necessary for a new portion of sauce, so the cook can whisk in one piece of butter, or 100. The proportions are entirely up to the cook’s taste and needs. The consistency of beurre blanc is like that of thick cream, and can be made somewhat thicker by adding water-free clarified butter once the initial emulsion has been formed. The phospholipids and proteins carried in the butter’s water are capable of emulsifying two to three times the butterfat in which they’re embedded.