When she was a child, her granny would take the pot of porridge from the stove and wrap it in cushions and blankets to finish cooking. That, Sarah Collins realized in 2008, was actually heat-retention cooking, the world’s most ancient way of cooking.

Cooking “pits” show archeologists that an area was inhabited by humans, and many people still use earth ovens today. In 19th century Europe, “hayboxes” were a common slow cooking method which used hay or straw for insulation, and they became popular again during WWII as a way to conserve fuel. In the 1970s, another South African outfit had distributed a similar product called the “wonderbox,” which used bags filled with polystyrene chips.