Adjust oven rack to lowest level. Preheat to 200°C/400°F/gas mark 6
Line a large roasting tin/pan with baking parchment (which prevents the chips from sticking) and add the oil.
Heat in the oven for 10 minutes.
Meanwhile wash and peel potatoes. Slice into 1.25 cm (½ inch) thick rounds and then into 1.25 cm (½ inch) thick strips.
Bring a pan of salted water to the boil and then add the chips and parboil for 5 minutes.
Drain well and pat dry with kitchen paper.
Carefully add the chips to the hot oil, turning to coat.
Cook in the oven for 40 minutes, turning halfway through, until they are golden and crisp.