Ingredients
1.2kg/2lb 8oz potatoes, such as Charlotte or Belle de Fontenay
1 litre/1¾ pints groundnut oil
salt

Method
1. With a sharp knife, square the potatoes into rectangles and then cut them into chips about 1cm/½inch thick. The length of the chips is not so important, but try to keep them the same thickness so that they will cook at the same rate.
2. As soon as the chips are cut, put them into a bowl under cold running water for 10 minutes or so to rinse off some of the starch, then drain them.
3. Next, bring a casserole of unsalted water to the boil and plunge in the drained potatoes. Bring back to the boil and simmer very gently until the point of a knife will penetrate the chips easily.
4. Very carefully lift the potatoes out of the water, using a slotted spoon, and place them on a tray. Allow them to steam until they are cool, then place them in the fridge. The chips will harden when cold.
5. Heat the groundnut oil to a temperature of 130C/250F (CAUTION: Hot oil can be dangerous. Do not leave unattended) and carefully plunge in the chips as they may splutter. After a while, they will take on a drier appearance (do not let them brown at all). When this happens, they have finished their second cooking process; drain them, let them cool to room temperature, and put them into the fridge. When cold, they are ready for their final cooking.
6. Heat the groundnut oil to a temperature of 180C/350F (CAUTION: Hot oil can be dangerous. Do not leave unattended). Carefully plunge in the chips and cook until golden brown. This may take 8-10 minutes.
7. Drain and season with salt only; they will take quite a lot. Serve.