Peel the potatoes, then cut into large chips. Rinse under cold running water until they run clear, then blanch in a large pan of boiling water for three minutes. Drain well, and cool on a large tray until they stop steaming, then chill in the fridge for approx 30 minutes.
Heat the over to it's highest possible setting, ideally about 250C, 230C fan, gas mark 9. Preheat a large, lipped, baking tray. Put the chips into a bowl, drizzle with the oil, and toss them around until well coated, then season well. Turn onto the baking tray, keeping them in one layer, then bake for 15-20 minutes, turning at least once, until brown and crisp.