Soak the mangoes for a few hours in water. Wash well; remove any dried sap.
Dry them thoroughly and cut the mangoes into quarters. Discard the seed. Remove the white skin that is attached to the kernel.
Now spread them out on a towel to dry for a few hours (either under the fan or in the sun).
Sun dry your spices like mustard seeds, fenugreek seeds etc. so that they have no moisture.
Powder mustard seeds in a blender. Add chilli powder and salt and mix well.
Now add fenugreek seeds and garlic to this spice mix and add half the oil. You will get a mix that is slightly wet. It must not be runny.
Now take a few dry mango pieces at a time, coat them with this spice mix and then put them in a barni (earthenware or ceramic container used for pickles).
Repeat this till all the pieces have been well coated. Any leftover spice mix can be added on top of all the pieces.
Add some more oil on the top. Save the leftover oil for later.
Now close the lid and tie it with a muslin cloth. Leave it in a dry, dark place for 4 days. After 4 days, open the pickle jar.
You will find that the volume of the pickled pieces must have come down by half. Give everything a nice stir with a dry ladle or spoon.
You can use your hands as well. You will find that the pickle must have become oily by now. Taste it to check for seasoning.
You should not need to but if it tastes less salty, add some more salt. The oil must cover the pickle and float on top. If not, add the leftover oil that you saved earlier.
Now let the pickle mature for 4 more days after putting the lid on and covering it with a muslin cloth.
On the 8th day, open the jar and you can begin consuming the pickle. Always ensure that a layer of oil covers your pickle. This prevents it from spoiling.
Have it with your regular meal or like me with parathas and curd rice. It is delicious.
It will last you easily for a year. It generally gets consumed before that.