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This type of bain marie the French word for "water bath" provides gentle heat to a soup, sauce, or other dish while you're waiting to serve it. A tall stock pot or other cylindrical pan is best for this purpose. Fill it to full of water, or enough to reach halfway up the side of the smaller container. Heat to a rolling boil, then reduce until the water is simmering. Unlike a double boiler, a bain marie does not require a snug fit between the two pans. A metal pastry ring at the base of the pan can support a small container. If you are keeping several small dishes warm, you can even use one large sauce pan for all them, placing each on its own supporting ring. Alternatively, fold a towel and place it on the base of the large pan. This will insulate the food even better than water alone, and keep small containers from rocking back and forth. The water should reach partway up the sides of the small container, but not enough to spill over the top. Leave the food to warm until ready to serve.
Fill a large sauce pan partway full of water. Bring water to a simmer. Place a metal ring at the base of this pan. Place the smaller container inside the larger one.