Wash the pickle jars and sun dry the jar till completely dry with absolutely no moisture.
Heat the mustard oil till its smoking point. Turn off the heat and set aside to cool down.
Wash the mangoes thoroughly in water and pat dry with clean kitchen towel. Cut them into pieces with the kernel intact.
Clean the mango pieces with a clean cloth and spread them over a dry cloth or large platter or tray while you work on the rest of the pickle preparation.
Grind the dry red chillies, mustard seeds, fenugreek seeds to a fine powder. Transfer them into a bowl.
Add the kashmiri red chilly powder and asafoetida, mix well and set aside.
Add the clean dry mango pieces into a large wide vessel or bowl.
Add the spice mixture, salt and mix well with a clean and dry spoon or ladle.
Add half portion of mustard oil and mix well such that the mango pieces are coated nicely with the spice mixture.
Add the spice coated mango pieces into the clean and sterilized airtight jar.
Pour the meaning mustard oil on top and cover the pickle jar with the lid. Shake the bottle well.
Show the pickle in the sun for at least 1-2 weeks depending on the weather or how much the pickle is exposed to direct sunlight.
Open the pickle jar and mix the pickle with clean dry ladle or spoon carefully every 2-3 days.
Pour some oil if required on top as the pickle needs to be covered in thin layer of oil. Cover the jar tightly with lid.
After a week or two your mango pickle is ready for consumption. Remove a small quantity of mango pickle into a small pickle jar for everyday use.
Always use clean and dry spoon in every serving. Serve mango pickle with dal rice, chapati, roti, paratha etc.