Step 1: Preheat the oven to 200C with the fan setting. In a flameproof roasting tin or ovenproof sauté pan, heat half of the oil. Brown the lamb for 2 minutes on each side, then remove from the pan and set aside. Add the remaining oil to the pan, followed by the potatoes, and fry for 4-5 minutes until they start to turn golden brown. Stir in the rosemary and garlic, then return the lamb to the pan.
Step 2: After roasting in the oven for 20 minutes, sprinkle the tomatoes over the dish and drizzle with balsamic vinegar. Return to the oven for another 5 minutes until the tomatoes start to split. Take out of the oven and serve directly from the dish.