Place the coconut, green chillies and cumin seeds in a food processor with half the measured water and blend to a fine paste.
Place the mangoes in a heavy saucepan with the turmeric, chilli powder and the remaining measured water. Bring to the boil, add the coconut paste and stir to mix well. Cover and simmer over a medium heat for 10–12 minutes, stirring occasionally, until the mixture becomes fairly thick.
Add the yogurt and heat gently, stirring, until just warmed through. Do not let the mixture come to the boil or it will curdle. Remove from the heat and keep warm.
Heat the oil in a small pan over a medium-high heat. Add the mustard seeds and as soon as they begin to 'pop' (after a few seconds), add the dried chillies and curry leaves. Stir-fry for a few seconds until the chillies darken. Stir the spice mixture into the mango curry and serve immediately.