If the pork shoulder comes with skin remove it and reserve to make crackling at another time (the skin won’t crisp here because this is a slow cooking process). You can even freeze the skin if you don’t want to make crackling now. For the dry rub, mix all the dry ingredients together. That is the brown sugar, the paprika, chilli flakes, black pepper, salt and mustard powder.
Rub the pork shoulder with the mixture making sure you cover the whole piece of meat.
Wrap with cling film and place it in the fridge overnight to marinade
Preheat the oven to 230 degrees Celsius (450 Fahrenheit, Gas Mark 8). After the resting period in the fridge and remove the cling film. Mix all the liquid ingredients in a bowl, except the ketchup. Roughly chop the onions and slice the garlic cloves (this doesn’t really need to be a fine chop).
Using olive oil, lightly oil a deep baking tray.
Place the pork in the middle and sprinkle the onions and the garlic all around. Pour a little of the liquid mixture over the pork and the rest on the sides (so you don’t remove all the dry rub from the pork). Cover with foil and as soon as you put it in the oven, reduce the temperature to 150 degrees Celsius (300 Fahrenheit, Gas Mark 2) . Let it cook for 6 hours. At the end of that time remove from the oven and let it rest for 30 minutes.
Sieve the sauce to remove the onions, garlic and general debris. To make a relish, add 2 to 3 tbsp of ketchup to the sauce with some of the onions and garlic and liquidise. Warm the sauce lightly if it’s gone cold.
Pull the pork meat using 2 forks and coat with the sauce throughout. Ready to eat!