Pat down the pork shoulder using a piece of kitchen roll especially on the skin.
Add plenty of salt and pepper to it all over focusing on the fat.
Measure and mix your rub ingredients together in a bowl and rub into the pork and set aside.
Peel and cut the onion, carrot and celery up into large chunks.
Put the pan on a high flame and when it's smoking hot, sear the meat in the pan with a drop of oil. Sear all over the meat, including the fat then set aside in the slow cooker.
Now turn the heat down to low, add the onions and a pinch of salt over them.
Peel and chop the carrots and celery into large chunks and add to the pan with the onions and fry until they're starting to go golden.
Chop the garlic cloves and add to the pan. Add the gluten free plain flour and cook it off.
Fry the veg until slightly golden in colour and the onions have started to caramalize.
Add in your beef stock and red wine into the pan and boil for about 5 minutes to cook the alcohol off.
Pour into the slow cooker around the pork, season and add the herbs and Dijon mustard.
Set the slow cooker on low for 8-10 hours or on high for 6-8 hours. Leave to cook.
Near the end of the cooking time preheat your oven at a very high temperature. I set mine as far as it would go.