1 tablespoon oil

8 cups hot water

1 1/2 teaspoons salt

2 stalks lemon grass (white part only)

4 lemon or other citrus leaves

2 or 3 fresh whole chilies

1 tablespoon fish sauce

2 tablespoons lemon juice, or to taste

1 fresh red chili, seeded and sliced

2 tablespoons chopped cilantro leaves

4 scallions (with green tops), chopped

Wash the shrimps heads well and drain thoroughly. Heat a saucepan with oil and fry the shrimps heads and shells of shrimps until they turn pink. Add hot water, salt, lemon grass, citrus leaves and whole chilies. Bring to the boil, cover and simmer for 25 minutes. Strain stock, return to the boil, add shrimps and simmer for 3 minutes or until shrimps are cooked. Add fish sauce and lemon juice to taste. This soup should have a pronounced acid flavor, so add sufficient lemon juice to achieve this. Serve in a large tureen or in soup plates, sprinkled with sliced chili, cilantro leaves and scallions.