You can make your own that is just as good as the expensive ones. Use a large pan and put 1 inch of water in the bottom and heat it to boiling, then reduce to a simmer. Use a large metal mixing bowl and put on top of the pan so that the steam is caught in between the two pans. This creates your double boiler.
DOUBLE BOILER: Place glass bowl over pan of very hot water, and whisk continually.
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