2) Place the pork, fat side up, on a clean baking sheet. Season the pork on all sides with salt and pepper then rub the dry rub all over the pork, pressing into the meat. Cover the pork with plastic wrap and place into the refrigerator for 7 hours.
3) Remove the pork from the refrigerator 30 minutes prior to cooking. Following the manufacturer's instructions and using lump charcoal and 75g drained wood chips for a smoker, or 150g for a barbecue, start the fire and bring the temperature of the smoker or barbecue to about 105C to 120C.
4) Place the pork on the rack in the smoker or barbecue. Cover and cook until an instant-read thermometer inserted into the centre of the pork reaches 75C. Turn the pork every 45 minutes, cook about 6 hours total.
5) If using the smoker, after 2 hours place the pork into the smoker pan and fill halfway with chicken stock to prevent the shoulder from drying out.
6) Add more charcoal, as needed, to maintain the temperature at 105C to 120C and more drained wood chips (75g for the smoker or 150g for the barbecue with each addition of charcoal) to maintain the smoke level.
7) Transfer the cooked pork to a clean baking tray. Allow to stand until cool enough to handle then shred into bite-size pieces. Mound on a platter and toss with most of the black pepper vinegar sauce, reserving the rest for drizzling the bun. Pour any juice from the baking tray over the pork.
Chef's Note: The pork can be made 1 day ahead. Transfer the pork and any juices to a baking tray, cover with foil and chill. Before continuing, re-warm the pork, covered, in a 180C/Gas 4 oven for about 30 minutes.
To assemble the sandwich:
1) Drizzle the black pepper vinegar sauce on the top and bottom of the bun. Top the bottom half of the bun with a generous helping of the meat.
2) Add another drizzle of sauce, a helping of the spring onion coleslaw and finish with the top of the bun.
For the black pepper vinegar sauce:
1) Place all the ingredients into a blender and blend until emulsified. Add water if the sauce is too thick.
For the spring onion coleslaw:
1) Place the spring onions, vinegar, chillies, mayonnaise, salt, pepper and oil into a blender and blend until emulsified.
2) Place the cabbage and red onions in a bowl, add the dressing and stir until combined. Fold in the coriander and season with salt and pepper, to taste.