1 lb (500g) shell-on prawns
2 pints (1.1 litres) fish stock
1 in (2.5cm) cube root ginger, peeled and cut into very thin matchsticks
Juice of 1 large lemon
Chopped chives and 2 tablespoons thin natural yoghurt or cream to serve
1. Peel the prawns and set them aside.
2. Simmer the heads and shells in the stock for 5 minutes.
3. Strain thoroughly through a sieve, making sure that the stock is really clear.
4. Simmer the ginger in l in (2.5cm) of this stock for 5 minutes, then strain, reserving the ginger.
5. Return the ginger flavoured stock to the pan of stock and bring to the boil.
6. Beat the eggs in a bowl with the lemon juice, then pour 2 tablespoons of hot stock into the mixture and beat well.
7. Remove the stock pan from the heat, add the egg mixture and stir with a balloon whisk.
8. Return the pan to the heat and cook very gently as the soup thickens to the consistency of thin custard.
9. Do not let the soup boil, or it will curdle.
10. Cool the soup, then chill thoroughly in the refrigerator.
11. To serve, pour the soup into shallow soup bowls and add the reserved prawns and ginger matchsticks.
Garnish with chives and a swirl of yoghurt or cream.