1/3 cup raw cane sugar, such as Demerara or turbinado (see Notes)
4 cloves garlic, minced
1 teaspoon dried oregano
1 teaspoon freshly ground pepper
1/2 teaspoon salt
1/3 cup cider vinegar
1 cup chili sauce, such as Heinz
1 1/2-3 teaspoons minced chipotle chile in adobo sauce (see Notes)
3 pounds boneless pork shoulder or blade (butt) roast, trimmed
Heat oil in a large skillet over medium-high heat. Add onions and cook, stirring occasionally, until they begin to soften, 3 to 6 minutes. Add sugar and continue to cook, stirring constantly, until the onions are golden brown, 6 to 8 minutes more. Add garlic, oregano, pepper and salt and cook, stirring, for 1 minute. Add vinegar and bring to a boil. Cook until mostly evaporated, 30 seconds to 1 minute. Remove from the heat and stir in chili sauce and chipotle to taste.
Place pork in a 4-quart (or larger) slow cooker and cover with the sauce. Cover and cook until the pork is almost falling apart, about 4 hours on High or 8 hours on Low.
Transfer the pork to a cutting board and shred using two forks. Stir back into the sauce.
Variation: Turn 3 cups leftover pulled pork into Pulled-Pork Torta. Preheat oven to 375°F. Coat a deep-dish pie pan or other 9-inch round baking dish with cooking spray. Heat 3 cups finely shredded Pulled Pork with Caramelized Onions (including sauce) just until warm. Drain one 14-ounce can no-added-salt diced tomatoes (reserve juice); combine with 1/4 cup diced Spanish-style chorizo (see Note) or pepperoni in a bowl. Mix well. Spread about 1/2 cup of the mixture in the prepared pan to cover the bottom. Top with one 8-inch flour tortilla (preferably whole-wheat). Spoon one-third of the remaining mixture over the tortilla. Top with another tortilla. Repeat twice, topping with a fourth tortilla. Drizzle the reserved tomato juice over the top and cover with foil. Bake for 20 minutes. Remove the foil, sprinkle 3/4 cup shredded Monterey Jack cheese on top and continue baking until the cheese is melted and the torta is bubbly, about 20 minutes more. Let cool for 10 minutes. Serve sprinkled with 1/4 cup each finely chopped scallions and chopped fresh cilantro, if desired.