The potatoes are covered with a layer of hot stones forming an oven.
Finally, banana leaves are layered over the whole thing in alternating directions to seal the motu oven. The leaves preserve the heat and also add some moisture to the process, resulting in potatoes that are both steamed and roasted.
After several hours, the stones have cooled, the process is reversed and the roasted potatoes can be removed. The final results are delicious -- soft and moist on the inside and delightfully smoky and crisp on the outside. Fish wrapped in banana leaves is also cooked on the stones, as are the local "puddings," a polenta-like dish made by grinding potatoes with coconut milk and steaming them among the "motu."
If it seems like these ladies are doing a lot of work for a simple meal, consider that before they can begin this cooking process, they have to dig up the potatoes, cut and carry the firewood, gather banana leaves, build a fire and move all those stones several times. Think of this the next time you stand impatiently in front of the microwave waiting for 2 minutes to pass!