Tom Yum Goong

Ingredients

• 500g whole raw head-on prawns
• 1.2 litres water
• 3 lemongrass stalks
• 6 slices galangal
• 8 kaffir lime leaves
• 200g oyster or straw mushrooms, halved
• 8 to 12 bird's eye chillies, bruised
• 60ml fish sauce
• 80ml lime juice
• 2 tsp sugar
• 2 tbsp Thai roasted chilli paste (nam prik pao)
• 2 tbsp neutral oil
• 3 tbsp evaporated milk, optional for the creamy version
• Handful coriander leaves

Before you cook

• Pull the heads from the prawns and set them aside, then peel the bodies and keep the shells
• Devein the peeled prawn bodies and refrigerate them
• Bruise the lemongrass stalks with the back of a knife and cut them into 5cm lengths
• Tear the kaffir lime leaves in half, leaving the tough central rib behind
• Bruise the chillies just enough to crack their skins
• Squeeze the lime juice only once the soup is nearly done so it stays bright

Steps

1. Heat the oil in a pot over medium-high heat and add the prawn heads and shells.
2. Fry them for four minutes, pressing the heads firmly with a spoon to squeeze out the orange fat.
3. Pour in the water and bring it to a boil, then lower the heat and simmer for fifteen minutes.
4. Strain the stock through a sieve into a clean pot and discard the shells.
5. Add the lemongrass, galangal and torn lime leaves to the stock and simmer for five minutes.
6. Stir in the roasted chilli paste until it dissolves and the broth turns a deep orange.
7. Add the mushrooms and bruised chillies and simmer for three minutes.
8. Drop in the prawns and cook them for ninety seconds, until they curl and turn opaque.
9. Take the pot off the heat before seasoning so the lime juice does not turn bitter.
10. Stir in the fish sauce, sugar and lime juice.
11. Taste and adjust: the soup should be sour first, salty second, with heat building behind both.
12. Stir in the evaporated milk now if you want the creamy nam khon style.
13. Ladle into bowls and scatter with coriander.