Prepare the potatoes and oil: In a 3-quart saucepan with a deep-fry thermometer attached, heat oil to 350 degrees F. Cut potatoes into long sticks -- about 2 inches by 1/2 inch. Lay potatoes in a single layer on paper towel. Let stand for 10 minutes until dry.
Cook potatoes: Toss potatoes with sugar. Fry half of the potatoes in the hot oil until they begin to crisp and turn light blond -- about 2 minutes. Use a slotted spoon to remove; drain on paper towel. Repeat for the second batch and let potatoes stand for 5 minutes.
Finish the potatoes: Raise oil temperature to 375 degrees F. Refry potatoes, in 3 batches, until golden brown -- 4 to 6 minutes. Use a slotted spoon to remove, drain on a paper towel, and sprinkle with salt.