NOTE: You can make this a few days ahead and store it in the fridge, but I prefer the night before you want to eat it.
Trim the skin and any large fat chunks off of the pork shoulder. Pat dry and set aside.
Put the onions, garlic and ginger on the bottom of the slow cooker. Evenly spread them out to create a bed for your pork.
In a bowl, mix together the chicken broth, 3 tbsp Worcestershire sauce, 1 tbsp molasses and 1 tbsp white miso. Whisk until thoroughly combined.
Pour this mixture on top of the onion mixture in the slow cooker.
In a separate bowl, mix together the dry rub ingredients until thoroughly combined.
Pat this dry rub all over the pork, on every side. Rub it into the meat. Use all of the dry rub.
Place the pork shoulder in the slow cooker, on the bed of onions and the chicken broth mixture.
In another bowl, whisk together the ingredients for the liquid glaze until thoroughly combined and there are no chunks of miso.
Pour this glaze onto the pork shoulder and rub it into the meat. The rest will fall into the slow cooking liquid.
Cook the pork on low for 8 hours, or on high for 6 hours. I prefer 8 for a low and slow tender meat.
When the meat is done, let it rest for an hour.
Shred the pork and discard any bones and large chunks of fat.