Tool: Double Boiler
A double-decker saucepan with an upper vessel that fits into a lower pot, which is filled with water. It's used to melt chocolate or cook delicate sauces without scalding. You can improvise a double boiler by putting a glass or metal bowl over a regular saucepan with water in the bottom. Be sure to have the water level low enough that it doesn't touch the bottom of the bowl. You want the heat to come from the steam, otherwise the temperature will not be evenly distributed.