Tom yumThai hot and sour soup

• 500 g1.1 lb large prawns, whole, heads and shells on (goong)
• 1.2 L5 cups water, or light chicken stock
• 3 stalks lemongrass, trimmed, bruised and cut in 5 cm (2 inch) pieces
• 5 cm piece2 inch piece galangal (kha), cut in thin slices, not peeled
• 6 makrut lime leaves (bai makrut), torn
• 3 cloves garlic, smashed
• 5 to 6 bird's eye chilies (phrik kee nu), lightly crushed; fewer for a milder soup
• 200 g7 oz straw or oyster mushrooms, halved or torn
• 2 small tomatoes, in wedges
• 1 small white onion, in wedges
• 4 tbsp fish sauce, to taste
• 1 tsp sugar, optional
• 4 to 5 tbsp fresh lime juice, to taste, added off the heat
• coriander leaves, to finish

Method

1. 1

   1. Peel the prawns, leaving the tails on, and devein them. Keep the heads and shells.

2. 2

   2. Bring the water to a boil, add the heads and shells and simmer for 5 to 7 minutes. Strain the stock back into the pot and discard the shells.

3. 3

   3. Add the lemongrass, galangal, lime leaves, garlic and chilies. Simmer for about 10 minutes, until the broth smells strongly of the aromatics.

4. 4

   4. Add the mushrooms, tomatoes and onion and simmer for 3 to 4 minutes, until the mushrooms soften.

5. 5

   5. Add the prawns and cook for 2 to 3 minutes, until pink, curled and firm. Skim off any foam.

6. 6

   6. Stir in the fish sauce and the sugar, if using. Take the pot off the heat.

7. 7

   7. Stir in the lime juice and the coriander. Taste: the soup should be sour, hot and salty in balance, so adjust with more fish sauce or lime. Serve at once with steamed jasmine rice.