Shell the prawns and simmer the shells in a pan with water, lime leaves, and peppercorns for five minutes.
Blend garlic, lemongrass, ginger, chilli, and coriander in a food processor to form a rough paste.
Strain the prawn stock through a sieve, discard the shells, and keep the liquid warm in the pan.
Heat olive oil in a large saucepan and fry the spice paste for two minutes before adding 300ml of stock.
Add coconut milk, salt, mangetout, and prawns then simmer for four minutes.
Divide beansprouts into bowls and pour the hot curry over them to serve.