Marinate the prawns with half the amount of salt and turmeric powder, respectively, for 10 min. Lightly fry and keep aside.
In a “non-reactive” Kadhai, add oil and let it smoke. Add the mustard seeds.
When the mustard seeds sputter, add a mixture of tamarind pulp, sugar, rest of the salt, the remaining turmeric powder and 1/2 cup water.
When the contents of the Kadhai come to a boil, add the fried prawns and simmer the flame. Sauté for 2 min and then add the remaining warm water. Just bring this to a boil.
Sprinkle the freshly roasted and coarsely ground powder of cumin seeds, red chillies and Paanch Phoron. Give the contents of the Kadhai a good mix and switch off the flame.
Immediately transfer the Chatni into a non-aluminum serving bowl. Allow to cool at room temperature and serve it at the end of a Bengali meal, with steamed rice.
The _Chatni_is best consumed within a day. On standing for almost more than 24 hours, the acidity of the tamarind changes the texture of the prawns.