Parboil the potatoes in salted water until just cooked but not too soft. All to cool, peel and cut into either halves or quarters depending on the size of the potato. Score the outside of the potatoes with the tines of a fork.

Preheat the oven to 180 ºC.

Place the potatoes in a roasting tin with the butter, whole garlic heads and rosemary leaves. Sprinkle liberally with oil and duck fat.

Roast for approximately 1-1/2 hours turning occasionally and basting until crisp and brown. Season to taste.