Use russets. Peel if you must, slice them on the thin side, rinse and drain thoroughly. Blanch in oil (peanut is good, tallow is best) at a simmering boil until soft, then drain and set aside. You can refrigerate them for cooking later.
Heat oil until close to smoking. Quickly add the potatoes in small batches; the oil will roil furiously and can easily boil over. When potatoes are buoyant and crisp, drain, salt, and serve.