A double boiler setup is crucial when you're gently heating foods such as chocolate, eggs for custard, or certain sauces, but I don't do enough gentle heating to buy one, and you probably don't either. Luckily, you can make one from stuff you already have; all you need is a pot, a bowl, and a chopstick or wooden spoon.
Photo: Claire Lower
Simply simmer some water in a sauce pan, and place a glass or metal bowl on top, with a chopstick or wooden spoon nestled between the two to let the steam escape. (This is important, otherwise the steam will build up and escape in a manner most violent.) Place your delicate foods in the bowl, and let the not-quite-boiling water below heat your food indirectly.