• Heat the oven to 160C/140C fan/gas 3. Scatter the onions and bay leaves in the bottom of a medium roasting tin. Mix the mustard powder with the paprika, pepper and salt in a small bowl. Rub this all over the pork, making sure you rub it into all the crevices. Place the pork, rind-side up, on top of the onions. Pour the water into the bottom of the tin, wrap it well with tin foil and bake for 4 hours (this can be done up to 2 days ahead – simply cover the tin in foil once cooked, and chill until ready to barbecue or grill).
• In a bowl, mix the tomato ketchup, red wine vinegar, Worcestershire sauce and brown sugar, until well combined. Remove the pork onto a plate and pat it dry with kitchen roll, and set aside.
• Place the roasting tin on the hob, pour in the ketchup mixture and bubble vigorously for 10 to 15 minutes until thick and glossy. Remove the bay leaves and pour the sauce into a food processor. Blitz until smooth, then smear half the sauce mixture over the meat.

Finish on the barbecue:

• Heat the barbecue to high. Once hot, place the pork on skin-side down. Cook for 15 minutes until nicely charred, then flip over and cook for another 10 minutes. The meat will be very tender, so be careful not to lose any between the bars.
• Lift the pork onto a large plate or tray. Remove the string and peel off the skin. Using 2 forks, shred the meat into chunky pieces. Add 4 to 5 tbsp of the barbecue sauce to the meat and toss everything well to coat. Pile into rolls and serve with extra sauce and some coleslaw, if you like.

Finish under the grill:

• Alternatively, heat the grill to high, place the pork back into the roasting tin and cook for 10 minutes on each side, until nicely charred.
• Remove the string and peel off the skin. Using 2 forks, shred the meat into chunky pieces. Add 4 to 5 tbsp of the barbecue sauce to the meat and toss everything well to coat. Pile into rolls and serve with extra sauce and some coleslaw, if you like.