1) Preheat the oven to 220°C/ gas mark 8.
2) Steam the potatoes, whole, for 20 minutes, until they are still firm yet easily pierced with a fork. Drain.
3) Spray a baking tray with cooking spray.
4) Place a potato on the tray, cut a small cross about 1/2cm deep into the potato and crush the potato with the back of a wooden spoon to flatten into a patty about 1cm thick. Try to crush it just enough so it stays together with most of its skin intact. Repeat with the remaining potatoes.
5) Brush the tops of the potatoes with the oil, sprinkle with salt and bake for about 20 minutes, until crisp and golden.