For the curry paste
Nip off the stalks of the dried long red chillies, then cut along their length and scrape out the seeds. Soak the chillies in water for about 15 minutes until soft.
Drain the soaked chillies, squeezing to extract as much water as possible, then roughly chop. Rinse the dried bird’s eye chillies to remove any dust. Using a pestle and mortar, pound the long red chillies, bird's eye chillies and scuds with salt.
Add the remaining ingredients in the order they are listed, reducing each one to a fine paste before adding the next. Yields approximately 100 g, about 4 tablespoons.
For the curry of crab
Simmer the coconut milk, season with salt, one pinch of palm sugar, lemongrass, galangal and kaffir lime leaves. Add curry paste and continue to simmer gently for a few minutes.
Season with another large pinch of palm sugar, fish sauce and kalamasi juice, then continue to simmer gently until rich, creamy and slightly thickened.
Add crab meat and stir in 1/2 cup of coconut cream and shredded kaffir lime leaves. Leave in a warm place for at least 30 minutes. This will allow the curry to develop in taste. Spoon over reserved coconut cream and serve with rice.