Wrap each mango in hay and arrange in a basket, layer over layer. Keep for a day or two to make it tart and soft.
Remove the seeds from the whole chillies and cut each into two.
Fry asafoetida in gingelly oil and powder.
Splutter mustard and fenugreek in the left over oil. When it splutters, add turmeric powder and saute.
Remove from fire and add all the remaining ingredients. Mix and cool.
Arrange a layer of mangoes in a jar. Place a layer of masala over it. Go on layering till all the mangoes and masala are over with a masala later on top.
Close the jar with an airtight lid and allow it to mature for four or five days.
Strain boiled and cooled water into the jar so as to cover the mangoes. Add this water only after the mangoes have absorbed the masalas.