Cut the greenest mango you can find into bite-sized cubes. The one I found wasn't the greenest but it works. Reserve the mango pit for tok dal or mango dal.
Sprinkle 1 tbsp salt and the turmeric on the cubed mangoes, rub and let sit in the sun for a day or two. You basically want the mangoes to be as dry as possible before making the pickle. Water is the enemy of food preservation. I don't get a lot of sun where I live, so I skipped this step. I will tell you what I did instead in the next steps.
Dry roast red chilies, cumin seeds, panch phoron, and mustard seeds and grind into a coarse powder.
If you dry the mangoes in the sun first, heat all the mustard oil in a pan, temper with asafoetida, and then add the mangoes. If you don't have the option of drying mangoes in the sun first, heat half of the mustard oil in a pan. Temper with asafoetida, add marinated mangoes, and fry over high heat until the mangoes are slightly scorched. You want the mangoes to be touching the bottom of the heated pan to get that sear. You basically want to get as much moisture out from the mangoes as possible.
Add the ground spices and give a good stir.
Now add the remaining 2 tbsp salt. This may seem like a lot of salt for 1 mango, but remember salt is essential for pickling. Salt provides a suitable environment for lactic acid bacteria to grow, which gives the pickle the characteristic flavor and preserves the fruit. You want to taste the saltiness at this stage and add more salt if necessary.
If you had added only half of the mustard oil in order to scorch the mango cubes, you want to add the remaining mustard oil now. Allow all the spices to cook for 1-2 more minutes before removing from heat.
Once the mangoes have cooled down, transfer to a mason jar. It is important to store the pickle in a glass jar because glass is inert. There’s is no chemical interaction between the acidity of pickle brine and the container. Glass can be recycled by melting down into new jars without deterioration again and again.
Let the jar sit in a part of the house that gets the most sun. This will keep for a year but should be ready to taste after a month or two.
This recipe is for one mango but multiply/adjust the ingredients depending on how many mangoes you are pickling. You have to use your judgment, though. For example, you won't need two cups for mustard oil for 2 mangoes.