A bain marie is also known as a double boiler. Essentially, it is a way of heating or cooking food indirectly. The steam from barely simmering water provides a gently heat that is much easier to control for delicate ingredients. Fill a medium saucepan with an inch or 2 centimetres of water. Bring the water to a simmer and place a heatproof bowl on top. A clear glass bowl is best for this. You will need a heatproof bowl that can sit snugly in the saucepan so that it doesn't actually touch the water.   Follow the recipe to cook or warm the ingredients and be careful that the water doesn't burn dry or boil.