Article: Choose a medium or large sauce pan to form the base of your double boiler. This should be relatively tall, especially if you'll be using the double boiler for a recipe with a long cooking time. This can be any heat-proof container that fits snugly over the sauce pan, so most of the steam is trapped between them. There should be at least 4 inches (10 cm) of space between the bases of the two containers, and preferably more.  Aluminum, copper, and (non-stainless) steel all conduct heat quickly. These will provide the shortest cooking time and prevent hot spots from forming.  Stainless steel, heat-proof glass, and ceramic are best if you are cooking acidic ingredients, since they are non-reactive. They conduct heat more slowly, so be sure to stir frequently to avoid hot spots. Glass also makes it easy to check on the water level. Set aside the smaller container now that you've confirmed it fits. Fill the larger pan with about 1–3 inches (2.5–7.5 cm) of water, but make sure there is plenty of space between the water and the smaller container. If the two pans fit tightly together and there is not enough space between them, the steam buildup could cause an explosion.  Although an explosion is very unlikely, the risk increases for recipes with long cooking times. For these recipes, use containers that do not fit perfectly together, so steam can escape through the gap between them. Lift the pan to allow steam to escape if it starts to rattle. The longer the cooking time your recipe calls for, the more water you'll need. Place the larger pot on the stove and heat until boiling. Reduce heat to medium-low until the water reaches a steady simmer. Leave the smaller pot on the counter while you wait for the water to boil. If you heat it along with the larger one, the hot surface could burn your ingredients when you add them. Place your ingredients in the smaller container, then place the container over the simmering pot. Cook as directed in your recipe. Stir the ingredients to ensure they heat evenly.  Despite the name, a double boiler should stay at a low simmer. Reduce heat if the water starts to boil, and add a little hot water if it starts to boil low. If the sauce starts to seize up or stick to the pan, just pick up the smaller container and whisk for a minute to reduce the temperature. Remember that there is trapped steam in the double boiler, and that the base of the small container is very hot. Use pot holders or oven mitts, and tilt the container toward you so steam escapes on the opposite side.
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Place a sauce pan on the stove. Place a smaller pan or mixing bowl on top. Pour water into the large pan. Heat water to a simmer. Heat the ingredients in the smaller container. Remove the small container from the heat.