Choose potatoes of approximately the same size. Wash very well. Place in a mold with a thick bottom or in a baking tray with high edges. Add water. Cover with a lid and put on high heat. After boiling the water, reduce the heat to a minimum and leave the potatoes under the lid until cooked (about 15-20 minutes). Periodically check with a toothpick whether the potatoes are ready.
If the potatoes are ready, and the water is still left, then open the lid, make the fire to the maximum and wait until the liquid completely evaporates.