Marinate your fish steaks with salt and turmeric and set aside for 15 minutes.
In a pan, lightly toast your whole spices for the Bengali Garam Masala ( cardamom, cloves and cinnamon) until fragrant. Let them cool and then grind them to a powder.
In a heavy bottom pot, add the mustard oil and bring it up to temperature until hot and mildly smoky. This is an important step – making sure the oil is hot enough.
Add the potato wedges and season with salt. Turn them every minute or so until you get an even golden crust over it. Cover it to let some of the steam form and help cook the potato while also getting colour. You are not trying to cook the potato fully. Set aside. Repeat the process for the cauliflower florets. Set aside.
Add a bit more oil at this point and sear the fish steaks on both side until lightly golden (in a medium-hot pan this should take just about a minute on each side depending on the size of the fish. Set aside.
In the same oil, add your nigella seeds and green chilli, let them sizzle lightly. Add the chopped onion and cook until softened and starting to turn golden around the edges. Add the ginger garlic paste and cook until the raw smell goes away.
Add all the dry spices (turmeric, chilli, cumin and coriander powders) and let them nicely coat in the oil before adding the fresh tomato puree. It is important to cook the tomatoes until all their water has evaporated and you start to see that slick of oil on the sides. Taste the sauce at this stage and balance with sugar.
Add a bit of hot water to give you a saucy consistency. Bring back the potatoes, cauliflower and fish steaks into the sauce, and cook gently for about a couple of minutes so everything finishes cooking together. When almost ready, taste add salt if necessary. Sprinkle a generous pinch of the Bengali garam masala and turn off the heat. Let it rest for at least 20 minutes before serving. Steamed rice is the only real way to enjoy this curry.
