At the French Laundry, we use an awful lot of butter without serving a lot of butter because of a method and substance called beurre monté—a way of infusing meats and fish with the flavor of butter. We cook in it, rest meats in it, make sauces with it. It's an extraordinary vehicle for both heat and flavor. Here's what beurre monté is: a few drops of water and chunks of butter whisked over a moderate heat to melt the butter and keep it emulsified, in one piece and creamy. Solid butter is an emulsification of butter fat, water, and milk solids; beurre monté is a way to manipulate the emulsification into liquid form. Thomas Keller: Salt and SeasoningDelicious, Quick Side Dishes
Make the beurre monté close to the time it will be used and maintain it in a warm place. If you have extra beurre monté, it can be refrigerated and reheated to use as melted butter or it can be clarified.