Using a mandolin, thinly slice the potatoes. Put the potatoes in a container, cover with water and refrigerate for at least 24 hours.
Rinse the soaked potatoes under cold running water and then pat dry with paper towel. Pour the vegetable oil into a deep heavy-based saucepan, no more than one-third full, then heat to 170°C (325°F). Deep-fry the potato