Light your charcoal in the KUDU and let them burn to embers with a layer of white ash.
While the charcoal is prepping prepare your lamb racks with a light coat of olive oil along with coarse salt and pepper.
Score the fat side of the lamb to keep the meat from curling.
Adjust your grill height over the embers to high heat (approx 700 degrees).
Add the rack to the grill bone side down at first.
Once you have a nice sear on both sides raise to medium heat (approx 400 degrees).
Continue to rotate your lamb every few minutes until your food thermometer reaches 125 degrees.
Now raise your lamb racks all the way and rotate off the heat allowing them to rest and reach desired internal temperature. I prefer 135 degrees or medium-rare.
While lamb is resting place garlic, rosemary, lemon juice and stock to skillet and in skillet over high heat or 2 seconds, whisk in butter and allow ingredients to come together.
Remove lamb and serve with sauce.