Marinate the fish with turmeric powder, ½ tsp salt and 2.5 tbsp mustard oil. After around 30 min, add yogurt, homemade garam masala powder, raisins, red chilli powder and the onion-ginger-garlic paste to this. Smear the fish pieces well. Let the fish marinate for 20 min.
Add ½ tbsp mustard oil to a hot wok and wait till the oil reaches its smoking point. Add the bay leaf, whole cinnamon, cloves and green cardamoms. After a few seconds, add the cumin seeds and wait till the seeds turn brownish. Now add the marinated fish carefully (the contents may sputter from the wok, at this stage), along with all the marinade. Cover for 2 min, or until the sizzling stops.
Reduce the flame to the lowest. Add ¾ tsp salt and give the curry a gentle stir, taking care not to break the fish pieces. Cover and cook, ensuring from time to time that the fish pieces do not stick to the pan, until the yogurt mixture starts releasing oil and becomes almost dry. This will take about 10 min.
Add the green chillies and sugar and flip the fish pieces gently. Add a cup of water, stir and cover again. When the gravy starts boiling, switch off the gas. Garnish with crisp-fried onions.