Place the lamb in a large baking dish. Prick the leg 6 times with a sharp knife and insert the garlic cloves in the openings. Brush with butter then season with salt and pepper.
Bake in preheated oven and baste regularly with the juices. The cooking time will vary depending on the size of the leg. Here's a guide: approximately 30 minutes for 1kg, 40 minutes for 1.5kg and 50 minutes for 2kg.
15 minutes before the end of the cooking time arrange beans around the lamb. Mix to coat with the juice and keep warm until the leg is cooked. Attention do not overcook the meat should still be pink.
Allow roast to rest for 10 minutes before slicing. Garnish with diced parsley and serve beans separately.