Hand-cut French fries into 5/16-inch matchsticks. Rinse under cold running water then place in a bowl of cold water mixed with white vinegar and leave to soak overnight.
Drain and pat fries dry. Blanch French fries in a large pot of 325- 350ºF oil for 5 minutes to cook without color. Drain on a rack and allow to cool to room temperature.
Increase temp of oil to 375ºF and return fries to fryer. Cook 5 minutes to crisp. Drain and cool on a rack once more. Once fries are room temperature again, put back in oil for the final frying. Fry until golden brown and extra-crispy, 3-5 minutes then drain and dump directly into a large metal bowl.