I remember reading about this type of cooking in an old copy of The Mother Earth News magazine from the Seventies.
The article described bringing the contents of the pot to a boil, covering it with a tight-fitting lid, and placing the covered pot into a thickly blanket-lined cardboard or wooden box, folding the blankets over the top of the pot, and then putting a lid on the box or closing its flaps.
Do whatever you can to prevent or slow down heat loss and let it sit for a couple of hours, hopefully slow-cooking the meal the rest of the way.
It’s supposedly a pioneer (and older) kind of thing and was supposed to be a way to cook meals using less fuel, like proper stir-frying is supposed to do.
