1. Place the potatoes in a large saucepan and just cover with cold water. Bring to the boil then boil, uncovered, for 5 minutes.
2. Meanwhile, switch the oven to 220C/425F/gas mark 7 and place the oil or fat in a large roasting tin towards the top of the oven to heat thoroughly.
3. Drain the potatoes thoroughly (reserving the water for gravy, stock or soup). Return them to the pan in batches and shake vigorously to soften the edges, or you can scratch them with a fork.
4. Take the tin from the oven and add the potatoes. Turn them quickly in the oil then cook at the top of the oven for 50-60 minutes, turning once halfway through cooking until crisp and golden on the outside and soft in the centre. Drain and sprinkle with salt. Serve as soon as possible.