Ingredients
3 shallots, thinly sliced
1 1/2 stalks fresh lemongrass, bottom 6 inches only, finely chopped (6 tablespoons)
1 piece (2 inches) peeled fresh ginger, coarsely chopped
1 pound ground pork
1 1/2 teaspoons coarse salt
1/2 teaspoon freshly ground pepper
Vegetable oil, for brushing
1/4 cup plus 2 tablespoons fresh lime juice (about 3 limes)
1/4 cup Asian fish sauce
3 to 6 fresh Thai chiles (depending on desired heat), thinly sliced crosswise
2 heads Boston lettuce (6 medium cup-shaped leaves reserved, remaining leaves shredded crosswise)
1/2 cup fresh cilantro leaves
1/4 cup fresh mint leaves
Cucumber wedges, for serving (optional)
Preparation
Process 2 shallots, the lemongrass, and ginger in a food processor until finely ground. Transfer shallot mixture to a medium bowl. Using your hands, gently combine shallot mixture, the pork, salt, and pepper (do not overwork meat). Shape into 6 patties (3 to 4 inches in diameter). Refrigerate, covered, until cold, about 1 hour (or overnight).
Preheat grill to medium-high (if using a charcoal grill, coals are ready when you can hold your hand 5 inches above grill for just 3 to 4 seconds). Brush grill and burgers with oil. Grill burgers, flipping once, until cooked through, about 5 minutes per side.
Make salad: Stir together remaining shallot, the lime juice, fish sauce, and chiles in a small bowl. Toss together shredded lettuce, the cilantro, and mint in a medium bowl. Add dressing; toss.
Place each burger on a lettuce cup. Top with salad, dividing evenly. Serve with cucumber wedges, if desired.
