Meatballs:

• 1 pound ground pork
• 1 lemongrass stalk, bottom 5 inches only, smashed with rolling pin, then minced
• 1/4 cup chopped shallots
• 2 tablespoons chopped fresh cilantro
• 2 tablespoons fish sauce (such as nam pla or nuoc nam)
• 2 garlic cloves, chopped
• 1 tablespoon vegetable oil
• 1 teaspoon sugar
• 1/2 teaspoon ground white pepper

Dipping sauce and assembly:

• 1 lemongrass stalk
• 1/4 cup fresh lime juice
• 1/4 cup fish sauce
• 2 tablespoons chopped fresh cilantro
• 2 tablespoons coarsely grated carrot
• 4 teaspoons (packed) golden brown sugar
• 2 teaspoons minced green Thai chile or serrano chile with seeds
• 2 tablespoons vegetable oil
• 1 head of butter lettuce, leaves separated
• 1 small persian cucumber, thinly sliced

For meatballs: 
Chill pork in freezer while making lemongrass paste. Combine lemongrass, 1/2 teaspoon salt, and remaining ingredients in processor; pulse until paste forms. Add chilled pork; pulse to blend. Shape into 24 balls (each about 1 tablespoonful). Place on rimmed baking sheet. Cover; chill at least 1 hour and up to 1 day.

For dipping sauce and assembly: 
Cut bottom 3 inches from lemongrass. Smash with rolling pin, then mince. Measure 1 tablespoon and place in small bowl (reserve the rest for another use). Add lime juice, fish sauce, cilantro, carrot, sugar, and chile to bowl; whisk until sugar dissolves.

Heat oil in large skillet over medium heat. Add meatballs; brown until cooked through, turning occasionally, about 15 minutes. Transfer to 1 side of large platter.

Arrange lettuce leaves and cucumber on platter with meatballs. Allow guests to place meatballs in leaves, garnish with cucumber, and drizzle dipping sauce over.