Grind the roughly chopped onions along with the ginger, garlic and chilis to a fine paste. Keep it aside, until needed
Apply the turmeric powder and half of the salt on your fish pieces. Heat the oil until it smokes and then lower the flame. Now add the fish fillets in batches and fry until they turn light brown on both sides. Remove and set aside
In the remaining oil add the whole spices and the dried chilis. When fragrant add the sliced onions and fry until they turn light brown
Then add the onion mixture paste, powdered spices along with 2-3 tbsp of hot water. Mix well and cook until you see oil leaving the sides
Lower the flame and add in the whisked yoghurt and stir in immediately to combine well
Add a cup of hot water, salt to taste and bring it to a boil, over medium flame, and gently drop the fried fish pieces in
Cover and cook for 5-6 minutes. Switch the flame off, drizzle the garam masala and coriander leaves over and mix gently
Keep covered for 5 minutes. Serve this lip smacking macher kalia (Bengali fish kalia) with steamed rice. Enjoy!