Cook the potatoes in boiling salted water until just soft, strain, leave to cool.
Cut the potatoes in half lengthwise. Spread the cheese, cured ham and rosemary over half of the potatoes, place the remainder of the potato halves on top. Secure the potatoes with a toothpick, and place them on a baking tray lined with baking paper and brush with oil.
Approx. 12 mins. in the centre of an oven preheated to 220°C.