Heat oven to 180C/fan 160C/gas 4. Heat a large heavy-based ovenproof, flameproof pan and add the oil. Drop the potatoes in the oil and cook for 5 mins, so they are coloured. Remove from the pan using a slotted spoon, draining the excess oil. Wipe the oil from the pan with kitchen paper, then return the potatoes to the pan. Put in the oven, and cook for a further 15 mins. Sprinkle over the mint and serve.