Dunk the mangoes for half an hour in hot water. Then roll them between your hands or on a hard surface till you feel them go squishy within the skin.
Remove the stem head with a knife, gently remove the skin and put skin in a bowl with 1 cup water.
Squeeze the pulp into the heavy bottomed pan in which the dish is to be prepared. Do the same for all the mangoes.
Squeeze the skin in the water and add the water to the mango pulp for cooking.
Simmer with salt and turmeric for 15 minutes on low flame till the raw flavour goes.
Add brown sugar.
Blend the chillies and coconut into a fine paste with half a cup water.
Add to cooked mango pulp.
Add yogurt and stir.
Turn flame high.
Keep stirring till the liquid starts bubbling around the sides of the pan.
Remove from flame or the yogurt will break.
Heat refined oil in a frying pan, put in the fenugreek seeds, wait till they change colour, put in the mustard seeds, switch off the flame when they crackle, drop in the curry leaves and broken chillies and stand back.
Transfer dish into serving bowl and top with the garnish.