Cook the baby new potatoes in salted boiling water until just tender. Cut the prosciutto slices in half lengthways and wrap one length around each new potato, tucking small sprigs of rosemary underneath, then secure with a toothpick. Place in a baking tray, drizzle with olive oil, then season well. Bake at 200C/fan 180C/gas 6 for 25-30 mins until very crisp and golden. Serve warm or at room temperature.