Chump of lamb is just restaurant-speak for lamb rump. We generally get it trimmed up with a small square of fat left on top. The meat is very tender and juicy and usually 250-300g (9-11oz) in weight. The garnish in this recipe works well with any cut of lamb from grilled cutlets to roast leg. I prefer to eat lamb on the medium side of medium rare, but cook it however you like. Buy the best-quality dried butter beans as you’d be surprised how the quality of dried beans can differ.