To make the coconut broth, whizz all the ingredients for the laksa paste to a fine paste in a food processor.
Twist off the prawn heads and peel away their shells. Heat 3 tablespoons coconut oil in a large, wide frying- pan over a high heat.
Add the prawn heads and shells and stir-fry briskly for 3 minutes or until they turn pink. Mix in the laksa paste and stir-fry for another 2 minutes.
tir in the coconut cream, chicken stock, kaffir lime leaves (if using), sugar, fish sauce and soy sauce. Bring to the boil, then simmer gently for 30 minutes. Strain and, once cool, cover and chill until needed.
Run a knife down the length of the back of each peeled prawn and remove the black digestive thread.
Set a frying pan over a high heat, add 3 tablespoons sunflower oil and, when hot, add a single layer of prawns. Fry briskly for 2 minutes, then turn and cook for another minute or until pink and cooked through.
Remove to a bowl and repeat with the remaining prawns. Cover and chill until needed.
To serve, warm 6 soup bowls. Place the broth in a large saucepan and set over a medium heat. Divide between 6 warm soup bowls.
Bring the broth to the boil and add the pak choy. As soon as it has wilted, add the beansprouts, spring onions and cooked prawns. Return to a simmer. Season to taste with the lime juice, ladle on to the noodles and serve immediately.