6 cups water
2 pounds boneless pork shoulder, cut in 2-inch pieces
1 medium onion, thinly sliced
1/4 cup cider vinegar, divided
1 teaspoon salt
1 tablespoon extra-virgin olive oil
1 cup finely chopped onion
4 cloves garlic, minced
1 (8-ounce) can tomato sauce
3 chipotle chile peppers in adobo sauce, finely chopped and mashed with a fork
1/2 teaspoon ground cumin
16 soft corn tortillas
16 green onions, trimmed
2 teaspoons extra-virgin olive oil
Salt to taste
Place 6 cups water in Dutch oven and bring to a boil over high heat. Add pork, the sliced onion, 3 tablespoons of the vinegar and salt. Return to a boil, reduce heat, cover partially and simmer 1-1/2 hours. Remove pork with slotted spoon and cool slightly; reserve 1 cup cooking water. Shred pork with 2 forks and set aside.
Place a 12-inch nonstick skillet over medium-high heat until hot, add oil and chopped onion and cook 3 minutes; add garlic and cook 15 seconds. Add tomato sauce, chipotles, cumin, remaining 1 tablespoon of the vinegar. shredded pork and 1 cup cooking water. Cook 1 to 2 minutes to heat thoroughly. Remove from heat, cover and let stand 10 minutes to absorb flavors. Place about 1/4 cup pork mixture and a roasted green onions (recipe follows) inside a roasted corn tortilla (recipe follows).
To roast green onions: Preheat oven to 425°F. Place green onions on a baking sheet, drizzle oil evenly over all and toss gently to coat. Arrange in a single layer and bake 10 minutes. Remove from heat, sprinkle with salt.
To roast tortillas: Char tortillas over burner or grill about 15 seconds on each side or until lightly charred.