Put the stock in a large pan, add the lemongrass, ginger and spring onions, and bring to the boil.
Stir in the rice and return to the boil, then reduce the heat. Cover and simmer gently for 8 minutes.
Season, then add the vinegar, prawns and bean sprouts. Return to the boil and simmer for 1 minute.
Pour the eggs into the simmering soup in a continuous drizzle. They should set into ribbons within a few seconds. Immediately, remove the pan from the heat and ladle into bowls. Drizzle each serving with chilli oil and serve immediately.
…speed it up
Ready-crushed lemongrass can be used to save preparation time – about 1 1/2 tsp should give a good flavour.
Crush the lemongrass with a rolling pin or the flat edge of a knife to release its delicate lemon flavour before adding it to the stock.