Add the join of pork shoulder (all fat and white bits removed) to the slow cooker with some sliced onion at the bottom. Then pour over the stock and all the rest of the ingredients, give this a stir and then leave this on low for 8 hours. Once the pork is tender and easily falls apart remove this from the slow cooker. Use two forks to shred this apart and then add the meat back into the sauce and leave this on warm whilst you prep the mac n cheese.