The Kochkiste, the cooking box, is a wooden box with a lid, almost a cube. A pot is brought to the boil on the stove and then put into the insulated box, where the food finishes cooking in its own heat.
It was promoted around 1900 as a kitchen aid that saved energy and money. A booklet of 1915, Die Kriegsküche, the war kitchen, showed it for energy-saving cooking. It came back when fuel was short, in the Second World War and during the Berlin Blockade of 1948 and 1949.