Place the pork shoulder in a slow cooker or oven and cook on low for about 4 hours, until the meat is very tender and easily shreds with forks.
Once cooked, remove the pork and let it rest for 15 minutes to keep the juices locked in. Then, shred the pork using two forks or your fingers for maximum control and messiness.
While the pork rests, slice the onion thinly and caramelize in a skillet over medium heat until golden and sweet-smelling, about 10 minutes.
Stir the shredded pork into a mixing bowl and add the barbecue sauce, tasting as you go to ensure a balanced smoky tang. Mix until well coated.
Toast the brioche buns until just golden and crispy on the edges, either in a toaster or in a hot skillet for about 2-3 minutes.
Quickly rewarm the shredded pork mixture if needed, then spoon a generous amount onto the toasted buns.
Top each sandwich with caramelized onions, then add slices of crispy pickles and a dash of hot sauce for extra flavor.
Serve immediately, with the first bite offering a perfect contrast of crunchy bun, juicy pork, and tangy toppings. Enjoy the messy, flavorful goodness!