Preheat oven to 350 degrees. Push garlic (3 to 4 slivers) into the shoulder of lamb. Cover with sprigs of rosemary, salt and a little olive oil. Roast uncovered for 3 1/2 to 4 hours. Remove lamb and leave to rest. Drain off the excess fat. Over the heat, add the flour to the pan of juices and cook for 1 to 2 minutes. Gradually add red wine or vegetable stock, stir until thick.