Cut potatoes lengthwise into about I"-thick strips and soak in a large bowl of cold water for 30 minutes. Drain, rinse under cold running water, then dry thoroughly with paper towels.
Pour oil into a large deep heavy-bottomed pot to a depth of 2" and heat over medium heat until temperature reaches 325º on a candy thermometer. Working in small batches, fry potatoes, stirring occasionally with a slotted spoon, until pale golden and crisp, 5–8 minutes. Transfer potatoes with slotted spoon to paper towels to drain. Season to taste with salt. Serve with grilled chicken with chile sauce and lettuce, tomato, and onion salad.