Wash and clean the prawns thoroughly and set aside.
Take a vessel, fill with water till it reaches half. Bring the water to a boil and add salt and vinegar to it.
To this water add the prawns. Cook for 3-4 min. Drain the water from the prawns.
Take a deep bottomed vessel, add oil for deep frying. Add the prawns to the oil and dry fry until golden brown.
Peel and slice garlic and ginger into thin strips. Set aside.
In a pan, dry roast 1 tsp mustard and ¼ tsp fenugreek seeds for 3 min. Let it cool.
Grind mustard seeds, fenugreek seeds and pink rock salt to a fine powder and set aside.
In a deep bottomed pan, add sesame oil and 1 tsp mustard seeds. Fry until the seeds sputter. Add the sliced ginger and garlic, fry for 2 min.
Add red chilli powder, mustard seeds, fenugreek seeds and pink rock salt powder, asafoetida and lemon juice. Mix well and cook until you can see the oil floating on the top.
Add the prawns to the mixture, mix well and cook on low heat for 2-4 min.
One it cools down, transfer to a jar. The shelf life of the pickle is 2-3 months if stored in an refrigerator. This pickle goes well with hot rice and ghee.