Sear the seasoned lamb shoulder in a very hot casserole pan until golden; this is a very important stage, as it will add flavour, then cook the onion, carrot and rosemary for 5 minutes until softened.
Stir through the puree for 1 minute then add the mint sauce, Worcestershire sauce and stock, give a good stir then place on a lid and cook in an oven set at 150℃ / gas mark 2 for 3 hours. Remove from the oven and use a couple of forks to shred the meat slightly.
Make the mashed potato of if you are using my cheat of shop bought mash pop this in the microwave for 3 minutes, stir well then spread this on top of the lamb mixture. Texture with a fork then sprinkle on the cheese. Turn up the oven to 180℃ / gas mark 4 then place back into the oven uncovered for 20 minutes. Leave to stand for 10 minutes before serving.