Shell the coconut, and cut the flesh into small pieces. Cut the stalks off the fresh chillies and then roughly chop.
Add to a blender with the coconut chunks, peanuts, 1 teaspoon of sea salt and 150ml of water. Blend until the mixture is fine.
Add the yogurt and blend again to a smooth paste. Transfer the mixture to a bowl.
In a small pan, heat the oil over a low heat. Add the mustard seeds, dried red chillies and curry leaves and cook until the seeds begin to pop.
Tip the tempered spices and the oil into the coconut chutney and mix well. This chutney will keep, refrigerated, in an airtight container for up to 2 days.