In a small bowl, mix together the sugar, chipotle, onion powder, garlic powder, smoked paprika, black pepper, and 1 tablespoon of kosher salt. If the pork is tied, untie and unroll it. If there’s a thick layer of fat, score it with a sharp knife. Rub the spice mixture all over the pork. To marinate the meat, place the pork fat side up in a Dutch oven or heavy pot (if it fits in your refrigerator), cover, and refrigerate. Alternatively, use a bowl or a resealable plastic bag. Marinate for as long as possible, ideally overnight or up to 1 day.
For a smoky flavor, you can smoke the pork for about an hour on a charcoal grill set up for indirect grilling with wood chips. Then transfer it to a Dutch oven or pot, cover, and proceed with baking as instructed. If not smoking the pork, cook it directly in the oven. About 4 hours before serving, preheat the oven to 425°. Let the pork sit at room temperature while the oven heats. Place the pork fat side up in a Dutch oven or pot if needed. Scatter onion around the pork, sprinkle with salt, and drizzle oil over the meat and onions.
Roast the pork for about 20 minutes until the onion browns and the pork fat starts to crackle. Meanwhile, remove the stems from the chiles, break them in half, and shake out the seeds.
Place the chiles on top of the browned onions. Add 2½ cups of water, cover the pot, and reduce the oven temperature to 300°. Cook for about 3½ hours, until the pork is tender and easily falls apart with a fork.
Transfer the pork to a sheet pan. For crispy bits, broil the pork until it’s deeply browned in spots, being careful not to burn it. While broiling or resting the pork, stir vinegar into the hot cooking liquid. Blend the liquid until smooth, skimming off any fat if desired. Taste and adjust with more sugar, vinegar, or salt. Return the pork to the pot and shred it using two forks. Pour enough of the blended sauce over the shredded meat to coat it evenly and stir to combine. If the mixture has cooled, reheat it over low heat until simmering. Serve the pulled pork hot, with extra sauce on the side. This dish can be stored in the refrigerator for up to 3 days or frozen for up to 3 months. Reheat by stirring occasionally in the microwave or over medium-low heat on the stovetop.