In a shallow pan, deep fry the fish pieces in gingelly oil until it is crispy and brown. Please do this in batches so each fish piece is not crumbled or broken. We need to take all the moisture from the fish, so that the pickle can be kept longer.
Turn off the burner and add red chilly powder, turmeric powder, fenugreek Powder, asafoetida . Put on the burner again on low flame fry this spice mix for few seconds till the raw smell of chilly powder goes and nice aroma comes. Please make sure not to burn the chilly powder.
Now to this mixture, add vinegar, water and salt, allow it to boil.
When boiled add the fish pieces into it and simmer for another 5-7 minutes. If you feel the gravy is too thick and not sour, again add hot water and vinegar and, bring it to boil once again. Turn off the burner.
Now check the taste, if you feel it¦s not too spicy , fry little more chilly powder in a separate pan and add to this and taste.
Now for the aroma and taste-roast 1/2 tsp mustard,1/4 tsp fenugreek seeds and + cumin seeds. Please use no oil to roast. When this is cooled down, grind it.
Sprinkle this roasted powder over the pickle & mix it well.
Now heat gingelly oil in a pan and allow it to cool. Add this to the pickle. This gives the pickle a protective layer to preserve. Store in an air tight glass bottle.
The spice level can be adjusted according to your taste.