Day 1 : Mix all the ingredients for the Dry Rub and rub into the pork, Place in bowl, cover and leave in fridge overnight.
Day 2: Remove pork from fridge and allow to stand for an hour at room temperature. Heat some oil in a large frying pan, and sear all sides of the pork on high heat.
Place the onions and garlic in an even layer in the slow cooker and pour in the stock or broth. Place the meat on top of the onions and garlic. Cover and cook until the pork is fork tender, about 6 to 8 hours on high or 8 to 10 hours on low
Make the Barbeque sauce by mixing and heating all the ingredients until the sugar disolves. Let cool.
Turn off the slow cooker and remove the pork to a cutting board. Set a fine-mesh strainer over a medium heatproof bowl. Pour the onion mixture from the slow cooker through the strainer and return the solids to the slow cooker. Set the strained liquid aside.
If the pork has a bone, remove and discard it. Using 2 forks, shred the meat into bite-sized pieces, discarding any large pieces of fat. Return the shredded meat to the slow cooker, add the barbecue sauce, if using, and mix to combine