Fill the bottom of your barbecue with sustainable lumpwood charcoal. Using a couple of natural firelighters, light the charcoal and allow it to heat until the coals are covered in a grey coat.
Clean the leeks then slice lengthways. Mix the butter, anchovy, butter, capers and thyme together with some salt and pepper and spoon into the leeks. Wrap the leeks in tin foil and place to one side of the embers. Rotate the parcel every 5 minutes, they will take around 30 mins or until they are soft.
Season the rump with pure sea salt, then place onto the grill and leave for 6-8 minutes. Turn the rump tail over and caramelise for a further 6-8 minutes. Remove from the meat and allow to rest for another 10 minutes.
Remove the leek for the tin foil making sure you save some of the gorgeous butter to baste the rump.
Slice the rump with the grain, serve with the soft leek and dress with the leftover hazelnut butter.