Step 1

Soak the frozen prawns in a deep bowl of cold water to defrost for 10 minutes.

Step 2

Meanwhile, place the stock in a saucepan and bring to the boil. Add the chilli, mushrooms, lime juice, fish sauce, sugar and the white parts of the spring onion. Bring back to the boil, then reduce the heat and simmer for 1 minute.

Step 3

Drain the prawns and add to the stock. Simmer for another 2 minutes, until the prawns turn pink and are cooked all the way through.

Step 4

Pour the soup into a deep bowl and stir in the green parts of the spring onion and the coriander leaves.