Preheat the oven. Arrange a rack in the bottom third of the oven. Heat the oven to 425ºF/218ºC.
Clean the potatoes. Wash and thoroughly dry the potatoes.
Cut slices into the potatoes. Using a sharp knife, cut thin slices down each potato, stopping just short of cutting all the way through. The bottom of the potato should stay intact. You can rest the potatoes on a pair of chopsticks and use that as a guide for when to stop slicing (the chopsticks will prevent you from cutting all the way down through the potato). Space the slices about ⅛-inch/3.2-cm apart,
Brush the potatoes with oil. Arrange the potatoes onto a baking sheet and brush with half the olive oil, including the bottoms.
Season. Sprinkle the potatoes generously with salt.
Roast. Roast the potatoes for 30 minutes. Remove the potatoes from the oven and brush with the remaining oil. Make sure to brush the oil all over the potatoes, including the space between the slices. Continue roasting until the potatoes are completely tender and the tops have bloomed outward and turned crispy and deeply golden, for about 30 more minutes.
Serve immediately, while still hot and crispy.
Store. Leftover potatoes keep well in an airtight container in the refrigerator for 3-5 days.
Reheat in a 400ºF/204ºC oven until heated through and crispy again. The time will depend on the size of the potatoes.