In a deep, heavy-bottomed pan, combine the coarsely ground shallots, ginger, green chillies, turmeric powder, red chilli powder, Kashmiri chilli powder, coriander powder, a few curry leaves, 1 tbsp coconut oil and salt. Mix everything well.
Pour in the thin coconut milk. Stir gently to combine.
Place the pan over medium-low heat. Once the curry begins to simmer, carefully add the fish pieces and raw mango slices. Cook gently for 7-10 minutes, without stirring too much, so the fish remains intact.
Pour in the thick coconut milk and continue cooking over low heat for 3-4 minutes until the fish is just cooked through and the gravy has thickened slightly. Avoid boiling vigorously after adding the thick coconut milk.
In a small pan, heat the coconut oil. Add the sliced shallots and a few curry leaves, and fry until the shallots turn golden brown and fragrant.
Pour this tempering over the curry and immediately switch off the heat.
Cover the pan and let the curry rest for 10 minutes before serving. This allows the flavours to meld beautifully. Serve warm with Kerala matta rice or steamed rice.
