Add potatoes to a large pot, cover with water and bring to a boil over high heat. Boil potatoes until they are fork-tender, about 15 minutes. Drain and allow to dry thoroughly, then cut into cubes.

Heat the oil with the butter over medium-high heat in a skillet. Add the potatoes, sprinkle on some salt and pepper and pan-fry until golden brown and crisp, 15 - 20 minutes.