A very good double boiler can be made by using a large outer boiler in
the bottom of which is placed a pot rest and a small amount of water.
Stand on the rest either one kettle well covered, or if necessary, two
kettles, one on top of the other, both tightly covered and the outer
boiler tightly covered. This arrangement forms a kind of fire-less
cooker which is exceedingly satisfactory, especially for cooking
cereals.