Soak potatoes in cold water to cover for a minimum of 1 hour and up to 24 hours. Drain and pat dry.
Heat 3 inches oil in a large stockpot to 275 to 300 degrees F. Line 2 baking sheets with paper towels. Blanch potatoes in small batches without crowding, turning occasionally, until completely cooked, but barely colored. Using a slotted spoon, transfer to 1 of the prepared baking sheets to drain in a single layer.
Increase oil temperature to 350 to 360 degrees F. Fry potatoes in small batches, turning occasionally, until crisp and golden brown. Using a slotted spoon, transfer to prepared baking sheet in a single layer. Sprinkle with salt and serve immediately.