Heat 1 tbsp of mustard oil in a pan on medium heat. When hot add the fish to the oil and fry for 3-4 minutes on both sides until cooked. Drain and remove from the pan and keep it aside. When cold roughly break it into small pieces.
Add the rest of the oil in the pan and add the chopped onion and saute until soft and turns golden brown.
Add in the chopped ginger, garlic and green chillies and continue sauteing on medium heat for 2-3 minutes.
Now add in the turmeric powder, chilli powder, cumin powder, coriander powder, black salt and bengali garam masala along with 2 tsp of water. Mix everything well and saute for a minute.
Next add in the boiled and mashed potatoes and mix everything well.
Now add in the shredded fish pieces and mix it well with the potato masala. Saute for a minute.
Finally stir in the coriander leaves and take it off the heat.
When the mixture is cold enough to handle, divide it into 9-10 balls and mould them into any shape you desire. I have made them in cylindrical shape as this is how it is made in Kolkata.
Now break 2 eggs in a bowl with a pinch of salt and whisk them nicely and place bread crumbs on a plate and keep it side by side. We are going to coat the patyNow dip a patty in the beaten egg. And then drain off the excess egg and place it in the bread crumbs and roll it until it is coated well with the bread crumbs. Again dip the patty in the egg and coat it well with the bread crumbs.
Again dip the patty in the egg and coat it well with the bread crumbs. Continue the same process with the rest of the patties and keep it on a plate. Now put it in a refrigerator for 15-30 minutes to set.
Heat oil on medium heat to deep fry the chops. Now fry the breaded patties in hot oil in batches for 3-4 minutes until it is golden brown in colour.
Remove it from the oil and drain it in a kitchen towel.
Serve it hot with some kasundi or ketchup.