For the sauce combine all ingredients into a deep bowl and mix.
Cover the exposed lamb bones with foil so that they don’t burn and ruin the taste of the lamb. Pick the rack up by the bones and give it a full dunk into the sauce being sure to coat both sides of the meat evenly. Set the racks on a clean baking tray. Prepare barbeque for indirect cooking at 350°F (175°C).
Leave 2 burners on and 1 burner off. Slide a drip pan under the burner that is off. Place the lamb over the drip pan on the off side of the barbeque. Close the lid and cook the lamb for 12-14 minutes (depending on the size of the racks) for medium rare. Lamb is cooked medium rare when a thermometer inserted in the middle of the rack reads 125°F (51°C). Be sure that the thermometer is not resting against the bone or the temperature reading will be inaccurate.
Remove lamb and tent it with tin foil for 10 minutes before slicing between the bones and serving.