1. Cut potatoes into halves, or quarters if large. Tip into a large pan of boiling, salted water. Bring back to the boil and cook for 7 mins. Drain well, then return to the pan and sprinkle over the flour. Place a lid on top, then give it a few hard shakes so the potatoes get bashed around.
2. Heat oven to 190C/170C fan/gas 5. Spoon the oil onto a large, lipped baking tray and leave on the top shelf of the oven for 5 mins. Carefully pull out the tray, make sure its surface is evenly coated with the fat, then tip on potatoes. Roast for 20 mins, then turn oven to 220C/200C fan/gas 7 and roast for another 30 mins, turning the potatoes once, until golden and crisp. Sprinkle with a little salt and serve straight away.