4 russet potatoes 2 1/2 quarts vegetable oil Coarse salt
Peel potatoes. Using a mandoline fitted with the zigzag blade, slice potatoes 1/8 inch thick, rotating them a quarter turn after each slice to create a waffle pattern. Soak slices in cold water 1 hour.
Fill a 6-quart heavy-bottomed pot with 2 1/2 quarts vegetable oil, and heat over medium-high until it reaches 365° on a deep-fry thermometer.
Meanwhile, drain potatoes; blot dry with paper towels. In batches, fry potato slices until golden brown, 1 to 1 1/2 minutes. Drain on paper towels. Lightly season with coarse salt. (Adjust heat between batches, if necessary, to keep oil temperature at 365°.)