Rub the lamb with salt, pepper and dill. Place the meat on a rack and roast in a 1600 C oven for 1 hour or until an internal temperature of 600 C is reached. Remove meat from oven and rest for 15 minutes.
Meanwhile melt the butter in a sauce pan and sauté the shallots and cucumbers until tender. Add the beef stock, bring to a simmer and reduce by half. Puree the sauce in a blender or food processor and keep warm.
Carve the meat into 1 to 2 cm slices and serve 2 to 3 per portion with 60 ml of sauce.