Fry onions and celery till soft.
Add garlic, thyme and cayenne pepper and cook for 1-2 minutes.
Add all other sauce ingredients and mix well.
Add pork shoulder and coat with sauce.
Leave in slow cooker on high for 4-5 hours.
Remove skin. This should come away easily. Pull apart the remaining meat with 2 forks. Stir pulled meat through the sauce and leave in slow cooker for another hour.
Skim off excess fat.
If you don't have a slow cooker this can be cooked in the oven. Follow instructions above and put all ingredients into a lidded casserole dish. Place in preheated oven 150C/130C fan/gas 2 for 4-5 hours until the skin comes away easily and the meat can be pulled apart. Stir pulled meat through sauce and place back in the oven for 30 mins.