Grind mustard and garlic to a fine thick paste. You can soak mustard in little water for 15 minutes before grinding. (optional)
Clean fish pieces, drain the water completely. You can add head portion of the fish too, it tastes very good in this curry.
Heat up mustard oil, add fenugreek and nigella seeds. Then add the ground paste.
Fry on low heat for a minute, do not allow it to get brownish. Add grated or finely chopped tomatoes. Fry till tomatoes get softened.
Add coriander, turmeric and chilli powder along with salt. Fry till oil separates.
Fill some water in the mixer jar in which you had made the paste, pour that water containing masala in masala.
Add dry mango powder and fish pieces.
Add more water to adjust the consistency as you like. Simmer for 10-15 minutes.
When fish is cooked and gravy leaves the oil it's ready to serve.
