1 Spray the inside of a 6-quart or larger slow cooker with nonstick cooking spray.
2 Season the pork: Combine 2 teaspoons of the kosher salt and 1/2 teaspoon of the black pepper in a small bowl. Sprinkle it thoroughly over the pork, using extra salt and pepper if needed to generously cover all sides
3 Sear the pork: Warm the oil in a large pot, Dutch oven, or cast iron skillet over high heat. Be sure to turn the vent on and throw open the windows as we’re going to create a lot of smoke.
Once the oil is glistening, add the pork. It should sizzle immediately. Sear the pork for 3 to 5 minutes on all sides — you want a nice golden-brown crust on each side. Don’t force it along. If the pork sticks to the pan, wait another minute or two until it releases easily before turning.
Transfer the seared pork to the slow cooker.
4 Cook the onions: In the same pot used to sear the pork, add the onions and reduce the heat to medium-high. Cook until the onions soften up and begin to take on bit of color, about 5 minutes. Use the liquid the onions release to scrape up the delicious browned bits on the bottom of the pan as they cook.
Transfer the cooked onions to the slow cooker with the pork.
5 Add the remaining ingredients to the slow cooker: In a small bowl, whisk together the remaining 1 teaspoon salt, the remaining 1/2 teaspoon black pepper, the Dr. Pepper, brown sugar, BBQ sauce, soy sauce, honey, mustard seeds, chili flakes, Worcester sauce, and liquid smoke (if using). Pour this over the pork and onions. Scatter the crushed garlics around the pork.
At this point, you can cover the pork and place it in the fridge overnight, or until you’re ready to start cooking.
6 Cook the pork: Place the lid on the slow cooker. Cook for 8 to 10 hours – the longer the better.
7 Shred the pork and serve: Once the cooking is done, transfer the meat to a large serving dish using tongs. Scoop up all of the cooked onions and smashed garlic as well, as they’ll add a lot of flavor.
Use a pair of forks to tear and shred the pork apart. Stir in some of the cooking liquid, one tablespoon at a time, to make it extra saucy, and serve.
Leftovers will keep for 1 week refrigerated, or up to 3 months frozen.