Halve the potatoes, if they are too big, quarter them. Sprinkle the cut surface with the rosemary sprigs, lightly salt and pepper. Then cut off approx. 15 cm of aluminum foil and pour some olive oil in the middle of the foil. Place the potatoes on top of the oil and seal the foil above. Now place the potatoes on the grillage, cook for about 15-20 minutes over medium heat. The oil shouldn`t leak.
The potatoes taste best when the cut surface is brown and crispy. Alternatively, you can season with paprika and curry instead of rosemary.