Smear the mustard over all meat surfaces & drizzle with a little olive oil.
Place onto the top rack of the Weber and add 3 sprigs of fresh rosemary .
Close lid and cook for between 3-5 hours, checking on coals after 2-3 hours & restocking if necessary.
To prepare the Weber/kettle:
The Weber kettle must be out of a draught so that the heat can build up without being dispersed by breezes, bottom vents must be fully open.
Stack 30 (or so) heat beads into each side compartment with a turkey sized drip tray in between to catch the juices.
Fire up the heat beads and allow them to become bright red all over, then allow them to develop an ash coating (lid off at this stage) before placing the prepared whole rump onto the top rack immediately over the drip pan.
Open the vent on the lid and replace lid.
Don't remove it for at least 2 hours, then check the state of the coals. Remove rump and rack, disperse spent ash, add more coals (if required) heat them up as before (coals must get red hot & ashy BEFORE putting rump back in & replacing lid).
Replace the rump and cook for approx 1-2 more hours for medium rare- or use a meat thermometer.
Generally it takes around 3-5 hours to cook the whole rump - depending on the size of rump and the weather conditions.
One of the best parts is the leftovers - they make seriously wonderful sandwiches!