Instructions

1. Arrange a rack in the middle of the oven and heat the oven to 350ºF.
2. Prepare the following, adding each to a food processor fitted with the blade attachment as you complete it: Peel and coarsely chop 1 (2-inch) piece ginger (about 3 tablespoons). Trim and coarsely chop 1 lemongrass stalk. Peel 1/4 cup garlic cloves if needed.
3. Add 4 bay leaves, 1 tablespoon kosher salt, and 1 tablespoon whole black peppercorns. Pulse until finely chopped, about 20 (1-second) pulses.
4. Line a roasting pan with aluminum foil. Pat 5 pounds pork shoulder dry with paper towels and place in the pan. Rub all over with the garlic mixture. Place the pork shoulder skin-side up in a roasting pan and add 1 cup water. Cover the pan with aluminum foil.
5. Bake for 30 minutes. Pour 1 cup soy sauce into a small bowl. Brush the pork shoulder all over with soy sauce. Cover again and bake for 30 minutes. Brush again with soy sauce, cover, and bake for 30 minutes more. Brush again with soy sauce one more time (for a total of 3 times).
6. Bake uncovered, adding more water to the pan as needed, until the skin is crisp and meat is tender and pulls apart easily, about 1 1/2 hours more. If the skin is not crisp, continue baking as needed, checking every 5 minutes. Meanwhile, prepare the sandwich ingredients.
7. Split 6 to 10 French sandwich rolls in half with a serrated knife. Cut 1 large head romaine lettuce crosswise into 1/2-inch pieces. Prepare the following, adding each to the same medium bowl as you complete it: Halve 1 pint cherry tomatoes (or quarter if large), finely dice 1 small red onion, and seed and finely dice 1 medium cucumber.
8. When the pork is ready, remove the skin and place on a clean cutting board. Shred the meat into bite-sized pieces; discard the bones and any large chunks of fat. Drizzle any remaining soy sauce over the meat and toss to combine. Cut the skin into bite-sized pieces.
9. Place the rolls cut-side up on a baking sheet (toast in batches if needed). Bake until lightly toasted, about 4 minutes. Meanwhile, add 1/4 cup distilled white vinegar, 1 tablespoon granulated sugar, 1/2 teaspoon kosher salt, and 1/2 teaspoon black pepper to the tomato mixture and toss to combine.
10. Assemble the po-boys: Spread 1 tablespoon of the mayonnaise on each bottom sandwich half. Top each with about 1/2 cup of the meat and a few pieces of skin, 1/2 cup romaine lettuce, and 1/4 cup of the tomato salad. Close the sandwiches with the top halves of the roll. Cut each sandwich in half with the serrated knife.