Trim potatoes into 4-inch-long blocks. Using a mandolin, cut potatoes into 3/16-inch-thick sticks. Place in a strainer and rinse under cold running water. Transfer to a large bowl and add cold water to cover by 1 inch, then let soak in the refrigerator at least 4 hours or up to 24 hours. Drain potatoes and rinse again and then spread on a clean kitchen towel and dry completely, patting off as much water as possible.
In deep fryer, heat oil to 350 degrees. Fry potatoes in batches until light golden, about 1 minute. Sprinkle with salt while hot and serve immediately.