First, marinate the Bata fishes with salt and turmeric. The fish should be slit and then kept for 10 minutes.
Then fire up the earthen stove, heat up the kadai, and pour oil. Let the oil heat up. (Pro Tip: Heat mustard oil until it just smokes, then lower the flame. This way the raw pungency fades away.)
Add the Bata fishes to the oil. Fry until it’s brown and crispy. Once the Bata fishes are fried, take them out. (Pro Tip: Do not flip the fish pieces early. Wait till the skin releases from the kadai or else it will break.)
Add the black cumin and then the onion. Fry it lightly for 5 minutes until it’s light brown.
Add all the green chilies and salt as much as required. Add the ginger and garlic paste. Fry it for 5 minutes without water.
Add the turmeric and a little bit of water. Cook it well for 5 minutes.
Now add water as much as required according to desired consistency for the gravy and cover it with a lid.
Then, remove the lid and add the coriander powder. Mix it nicely.
When the spicy gravy starts to boil, add all the fried Bata fish pieces and a pinch of salt. (Pro Tip: Swirl the kadai instead of stirring the fish pieces. Fried Bata breaks very easily.)
After 5 minutes, Bata Macher Jhal is ready.