From the Seattle Times via Reddit.
Ingredients
For the roast pork:
3 1/2 pounds bone-in pork shoulder, or 3 pounds boneless
10 cloves garlic, coarsely chopped
1 1/2 tablespoons kosher salt
2 teaspoons freshly ground black pepper
2 cups orange juice
1/2 cup lime juice
2 tablespoons dark brown sugar
2 tablespoons chopped fresh oregano
1/2 cup extra-virgin olive oil
1 cup (about 1 large) diced onion
2 bay leaves
For the garlic mayonnaise:
2 tablespoons finely minced garlic
1/4 teaspoon garlic salt
1 cup mayonnaise
3 tablespoons sweet relish
1 teaspoon freshly squeezed lemon juice
For the sandwiches:
2 tablespoons extra-virgin olive oil
1 large yellow onion, cut into ¾-inch rings
Six 7-inch-long pieces baguette, split, toasted, and buttered
12 to 18 sprigs of cilantro
Pickled jalapenos
Romaine lettuce leaves
Instructions
1. In a large resealable plastic bag, combine the pork, garlic, salt, pepper, orange juice, lime juice, brown sugar, oregano, olive oil, onion, and bay leaves. Seal the bag and place it in the refrigerator for at least 4 hours, preferably overnight.
2. To make the roast pork, preheat the oven to 300 degrees. Remove the pork from the bag, reserving the marinade, and place the pork in a roasting pan. Pour the reserved marinade (including the bay leaves) into the roasting pan, and tent the pan loosely with aluminum foil. Roast the pork, covered, for 2 hours on one side. Flip it over and roast, uncovered, on the other side for another 1 1/2 to 2 hours, so the marinade has a chance to reduce slightly. After 3 1/2 to 4 hours, the pork should be falling-off-the-bone tender — if not, roast it for another 15 minutes and check again.
3. Remove the pan from the oven and let the meat rest for 20 minutes, covered. Remove the foil and shred the pork into large chunks directly in the pan, mixing the remaining marinade into the meat to make it extra moist. The pork should be slightly pink from the ultraslow cooking time, and the juices should run clear. (The pork can be made a day ahead — simply reheat at 350 degrees for 30 minutes the next day.)
4. To make the garlic mayonnaise, combine all the ingredients in a small bowl, cover, and refrigerate overnight so the flavors meld together.
5. To assemble the sandwiches, heat the olive oil in a small skillet over medium-high heat for 1 minute. Add the sliced onions and saute for about 4 minutes, until the edges of the onions just turn golden brown. (Alternatively, preheat the grill, toss the onions in the olive oil, and grill for 4 to 5 minutes, until the onions are lightly browned.)
6. Spoon a heaping tablespoon or two of the garlic mayonnaise on the top and bottom of the baguette pieces. Layer a few cilantro leaves and jalapeno slices on the bottom of the baguette pieces, then pile on a generous amount of pork (¾ cup of meat is a good place to start). Top with the grilled onions and a few leaves of romaine, and then squish the top of the baguette down onto the sandwich.