Remove all scales of the prawns or shrimps and wash it well. Marinate the prawns with a pinch of turmeric and a little salt.
Heat mustard oil in a deep pan. When hot, add the chopped onion and sauté it on low heat.
As the onion begins to turn brown, add the chopped potatoes. Mix everything. Add turmeric, kuti-mirch, and salt and mix some more.
Once it looks a little cooked, place the marinated prawns in the pan and stir. Add sliced green chillies. Stir slowly, and add water.
Cover with a lid and let the preparation cook for 5–6 minutes.
If the dish has come to a slight boil, mix well, add a little mustard oil, and cover for another 3-5 minutes. Chingri maach'er bati chorchori is ready when it comes to a slight boil again.