Delicate foods that cannot withstand direct heat frequently require cooking in a double boiler. Many kitchens are not equipped with this piece of special equipment, but you can use other items to create a makeshift double boiler.
Structure
A proper double boiler consists of two pans, one stacked on top of the another so that the top pan is suspended inside the bottom one. Water is placed in the bottom pan and the food to be cooked goes in the top pan. As the water heats to a slow simmer or light boil, it gently heats the contents in the pan above it without the perils posed by direct heat.
Substitutes
A heatproof glass, ceramic or metal bowl can be placed atop a pot with water in the bottom to create a double boiler effect. The bowl should be large enough to rest on the rim of the pot and not touch the bottom. A trivet made of materials similar to the bowl can suspend the bowl in the pot’s bottom to create the same effect.
Uses
Dairy-based sauces and custards tend to easily stick to pan bottoms. Chocolate melted over direct heat commonly burns or becomes grainy. A double boiler prevents these culinary catastrophes by avoiding direct heat contact from the stove burner.