Heat a BBQ to medium-high with the coals banked up one side, or with one of the gas burners on high with the others off (see cook’s notes). Sear the fat side of the steak for 2-3 minutes, directly over the heat, until golden, then sear all of the remaining sides for 1-2 minutes until dark and caramelised. Move the steak to the other side of the BBQ, fat-side down, and cook for 18-25 minutes with the lid closed, or until the internal temperature of the meat reads 50-55C. If the BBQ has a thermometer it should read 200C during this period. Move to a plate and rest for 10-15 minutes or until the internal temperature reads 60C in the thickest part, then slice against the grain.