Preheat oven to 180º C (ST: I leave the roasting tray in the oven to preheat that as well)
Boil the potatoes for 18 minutes until the potatoes start to disintegrate.
Pour off water (ST: I leave to cool a bit as well)
Transfer potatoes to the roasting tray
Pour oil over the potatoes
Roast for 50-60 minutes at 180º C, turning, until crispy all over (make sure it is a big pan)