Heat your oven to 160°C/Fan 140°C/Gas 3. Line a roasting tin with several sheets of foil so there’s plenty hanging out over the sides – enough to wrap loosely around the pork.
Pat the pork shoulder dry with kitchen paper. Place it in the middle of the tin. Mix the sugar, salt and paprika together and rub all over the pork. Pour 200ml boiling water into the tin (not over the pork). Pull the foil up and over the pork. Crimp it together to make a loose, sealed parcel.
Slow cook the pork in the oven for 4 hours. While it roasts, cut the plums in half. Scoop out the stones with a teaspoon.
Take the pork out and unwrap it with oven gloves – be careful of the hot steam. Turn the oven up to 220°C/Fan 200°C/Gas 8. Add the plums to the tin. Slide it back into the oven and roast for a 30 mins to crisp up the skin and soften the plums.
Lift the pork out of the tin onto a carving board. Snip off the string. Slice off the crisp skin and set aside. Pop the plums on a plate. Use two forks to pull the pork apart into shreds. Pour the cooking juices out of the tin. Wipe it clean. Pile the shredded pork back into the tin. Keep the skin separate so it stays crisp.
Dissolve the chicken stock cube in 200ml boiling water. Pour the stock over the pork. Loosely cover with foil.
Leave the pork to soak for 30 mins, then serve with the roasted plums.