Peel and halve the potatoes. Cook in a large pan of boiling, salted water for about 15 to 20 minutes or until tender. Drain, then, when cool enough to handle, cut into walnut-sized chunks.

Heat the oil and butter in a large frying pan and cook the warm potatoes in batches, tossing them frequently, for about 10 minutes or until they are evenly golden. Season generously with salt and pepper. Spoon on to sheets of kitchen paper to drain off any excess fat. Serve straight away.