Marinate prawns with turmeric powder and salt. Set aside for 10 minutes.
In a blender, combine onion, garlic, ginger, green chillies, and grated coconut (if using). Add a little water and blend into a thick, smooth paste.
Heat oil in a large pan over medium-high heat. Briefly fry the marinated prawns for 1-2 minutes until just pink. Remove and set aside.
In the same pan, heat remaining oil and add cardamom pods, cloves, and bay leaves. Fry for 30 seconds until fragrant.
Add the onion paste to the pan and sauté for 5-7 minutes, stirring frequently, until the mixture is golden and aromatic.
Add chili powder and salt, stirring for 1 minute to prevent burning.
Pour in coconut milk (if using instead of fresh coconut) and a little water if needed. Bring to a gentle simmer.
Return the prawns to the pan and simmer for 5 minutes until prawns are cooked through and curry has thickened slightly.
Garnish with fresh coriander and serve immediately with boiled rice.