In a food processor, blitz the chillies, onion and ginger with 3 tbsp water into a smoothish paste – you may need to scrape it down the sides.
Heat the oil in a heavy pan or wok. When hot, toss in the mustard and fenugreek seeds, and curry leaves – they’ll crackle and pop – and fry for 10 seconds. Add the onion paste, turn the heat down a tad and cook without colouring for about 5 minutes. Splash in some water if it starts to catch.
Add the turmeric and cracked peppercorns and stir the spices around for a few seconds before tipping in the
prawns. Pour in the coconut milk and bring to a simmer, stirring all the time. The milk will take on a yellow colour from the turmeric. Cook for 1 minute until everything’s heated through. Squeeze over some lime, sprinkle with fresh coriander and serve with rice.