A double-boiler is a stovetop apparatus used to cook delicate sauces
such as beurre blanc, to melt chocolate without burning, or for any occasion when more indirect heating is desired.
It consists of a saucepot of boiling water, on top of which a second pot fits, so that the latter is heated by steam.
If one does not own such a device, the same cooking technique can be achieved by placing a metal bowl or glass bottle in a larger pot of boiling water.
A similar device is the bain-marie.
Compare to double steaming.