Ingredients

• 2 fresh lemongrass stalks, root ends trimmed and 1 or 2 tough outer leaves discarded from each
• 2 garlic cloves, chopped
• 3 tablespoons chopped shallot
• 1 tablespoon finely chopped peeled ginger
• 1 (3-inch) fresh serrano or jalapeño chile, finely chopped, including seeds
• 1 teaspoon water
• 4 teaspoons Asian fish sauce, divided
• 1 1/2 pounds ground turkey (dark meat only)
• 1/4 cup fresh lime juice
• 1/4 cup vegetable oil
• 1/2 teaspoon sugar
• 1/2 teaspoon dried hot red-pepper flakes
• 4 kaiser rolls, split and grilled
• 2 cups mixed fresh mint, basil, and cilantro leaves
• Equipment: a mini food processor

Instructions

1. Thinly slice bottom 6 inches of lemongrass (1/4 cup), discarding remainder. Finely grind lemongrass, garlic, shallot, ginger, and chile with water and 2 teaspoons fish sauce in mini food processor, scraping down side frequently, until a paste forms.
2. Mix paste and turkey with your hands until just combined (do not overmix) and form into 4 (3/4-inch-thick) patties (4 inches in diameter). Chill patties, covered with plastic wrap, 1 hour (to allow flavors to develop).
3. Whisk together lime juice, oil, sugar, red-pepper flakes, 1/8 teaspoon salt, and remaining 2 teaspoons fish sauce until sugar is dissolved.
4. Prepare grill for direct-heat cooking over medium-hot charcoal (medium heat for gas).
5. Oil grill rack, then grill patties, covered only if using a gas grill, turning over once, until just cooked through, 10 to 12 minutes total.
6. Whisk lime-juice sauce, then drizzle cut side of a bottom bun evenly with 1 tablespoon sauce. Top with a patty and 1/2 cup mixed herbs. Drizzle herbs with 1 tablespoon sauce and top with bun. Assemble 3 more burgers in same manner.