Rinse lemongrass, crush with a heavy saucepan. Halve chili lengthwise, remove seeds and cut into thin strips.
Remove peel from ginger, also cut into strips as fine as possible. Clean and rinse spring onions and cut into pieces.
Coarsely chop lemongrass and heat in a saucepan with clear soup. Steep in the clear soup for about 20 min.
Sauté ginger, chili and spring onions in hot sesame oil. Pour clear soup through a sieve and season with soy sauce.
Cut the corn dumplings into bite-sized pieces and cook in the hot soup for about 5 minutes. Serve sprinkled with coriander leaves.