Place the lamb racks on a large tray or dish, and season well with salt and pepper on both sides. Drizzle well with olive oil to coat, also on both sides.
Roughly chop 6 sprigs of Rosemary, setting the other two aside. Sprinkle the rosemary and garlic all over the racks, then cover them and place in the fridge overnight.
Prepare a braai for two-zone cooking (see link above for instructions). Take racks out of fridge, and brush off the majority of the chopped rosemary and garlic.
Place the lamb racks on the indirect side, and braai for 20 minutes, then flip and braai the other side for 20 minutes, have the lid closed for both cooks.
Stoke the coals then throw the remaining rosemary sprigs directly on them, they will create 2-3 minutes of great rosemary-scented smoke (if you’re using gas, omit the burning rosemary and just turn the gas to highest setting). Immediately place the ribs over the direct heat, and sear for 4-6 minutes per side, until a nice char has developed.
Remove the racks from the braai, and place under foil to rest for 10 minutes. Then slice, serve and eat immediately.