Put the brown crabmeat, shallots, garlic and fish stock into a food processor or blender and process until smooth.
Tip the mixture into a pan and add the rice and crushed chilli flakes. Bring to the boil, then reduce the heat. Cover and simmer, stirring occasionally, for about 10 minutes or until the rice is just tender.
Stir in the fish sauce, coconut milk and lime juice. Add the white crabmeat and heat through gently. Season lightly. Ladle into bowls, then sprinkle with coriander and spring onions. Serve immediately.
If you have time, serve the soup with a dish of coarsely shredded or thinly sliced vegetables (such as carrot, celery, onion and cucumber) – just as they are or sprinkled with rice vinegar or white wine vinegar.
Buy ready-dressed crab from the fishmonger or supermarket and use within a day of purchase. * Avoid using frozen or canned crabmeat for this recipe as it has less flavour than fresh.