Wash the potatoes well and slice them in half. Put them in a heatproof container, add a little water, put the lid on and microwave them. When cooled, peel them and cut them into thirds.

Heat a frying pan, add the vegetable oil and potatoes, and fry until brown. Add butter halfway through, and let it blend evenly.

Fry until both sides are golden brown. Finally, turn the heat to high so the surfaces become crispy.

Season with salt and pepper to finish.