Cut the ends off the lemongrass, remove the outer layer, then roughly chop.
Put the shallots, garlic, lemongrass & fish sauce in a food processor and blend until they're finely chopped. Add the mint, coriander and cornstarch. Blend for several seconds, then add the mince. Season with salt and pepper and blend for a few seconds until well combined.
Shape 18-20 little balls from the mixture. Place these on a baking tray lined with baking paper, then grill for 3-5 minutes on each side.
Brush each ball with some chilli sauce and grill for a couple of minutes until lightly caramelized Serve with sweet chilli sauce.