Lamb Larb

Ingredients

• 1 lemongrass stalk
• 4 garlic cloves
• 1/2 bunch cilantro, stems and leaves separated, stems coarsely chopped, plus sprigs for serving
• 1 large shallot, coarsely chopped
• 4 red Thai chiles, divided
• 1/2 cup salted, roasted peanuts
• 3 tablespoons fresh lime juice
• 1 tablespoon (or more) fish sauce
• 1 1/2 teaspoons demerara sugar or dark brown sugar
• 2 tablespoons vegetable oil
• 1 pound ground lamb (at least 10% fat)
• Cooked white rice, Bibb lettuce leaves, sliced cucumber, lime wedges, and mint sprigs (for serving)