A preparation closely related to beurre blanc is beurre monté, “worked up” or “prepared” butter, which is simply an unflavored beurre blanc made with an initial dose of water rather than vinegar or wine. Beurre monté is used among other things as a poaching medium. Thanks to the relatively low heat conductivity and heat capacity of fat compared to water, it cooks delicate fish and meats more gradually than does a broth at the same temperature.
From the book On Food and Cooking (2nd edition) by Harold McGee. © 2004 Harold McGee. By permission of Scribner, a division of Simon & Schuster, Inc.