Peel the potatoes and cut into small pieces around two inches/5 cms square.
Put the oven on at 425°F/210°C/Reg7. Put oil into a roasting pan up to half inch 1.5 centimetres deep, add the butter and put into the oven. Meanwhile par boil the potatoes for 5 minutes.
Drain the potatoes in a colinder and shake to roughen up the surfaces of the potatoes. Season the potatoes lightly with salt and pepper and add to the hot oil/butter mixture using a spoon to thoroughly coat the potatoes with oil.
Turn the potatoes around every 15 minutes and cook for 45 to 60 minutes until golden brown all over. Remove from the pan with a slotted spoon or tongs shaking off the fat and put into a serving dish.