1 Rinse lemongrass, remove tough outer leaves and cut stalks into small pieces.
2 Peel ginger and coarsely chop. Rinse chile peppers, halve lengthwise, remove seeds and, if necessary, rinse again.
3 Heat 1 tablespoon oil in a pot over medium heat. Cook lemongrass until softened, 1-2 minutes.
4 Add ginger and 1 chile pepper and cook briefly. Pour in the fish stock, bring to a boil and cook over medium heat for about 30 minutes.
5 Meanwhile, squeeze out juice from limes. Rinse cilantro, shake dry, pluck leaves and chop coarsely. Clean mushrooms and cut into slices. Peel garlic and finely chop, then mix garlic with remaining chile pepper.
6 Pass soup through a sieve into another pot. Stir in the fish sauce, lime juice, coconut milk and sugar. Season with salt and pepper.
7 Add the mushrooms, garlic and chili pepper to the soup and reheat.
8 Rinse shrimp and pat dry with paper towels. Heat remaining oil in a pan over medium heat and cook shrimp until opaque, about 4 minutes.
9 Divide soup among 4 soup bowls or plates. Thread shrimp on 4 wooden skewers and arrange on the soup. Garnish with chopped cilantro and serve.