1) 3 Tbsp white mustard seeds
2) 1 Tsp ginger paste
3) 1-2 chilies
4) 1 Tsp mustard oil (for the paste), 1/4th cup mustard oil for cooking
5) 1/2 Tsp salt for the paste
6) 1 Tsp turmeric powder
7) Any fish, I used Salmon
8) Tomatoes, chillies, peppers, coriander leaves
1) Soak the mustard seeds in water for 2 hours
2) Drain the water and put in a blender
3) Add all other ingredients
4) Add 3 Tsp water and grind. Add more water if the mix gets too dry.
5) Grind until the paste is very smooth, fluffy almost.
7) Marinate the fish meanwhile in salt and turmeric powder.
Start by sautéing the fish in a little oil. If fish is not too fresh then deep fry it in oil.
In the same pan, sputter up some mustard seeds, add the pepper and tomatoes and chilies and sautée for a while. Then add the mustard paste.
Mustard paste gets bitter if fried for longer in oil. So if you intend to have a thick gravy, add the water to the paste before putting the paste in oil and tempering. If you intend to make a dry dish, turn of the flame before adding the paste and after the paste is all well mixed with the main ingredients, then turn on the flame again.
I have added the recipe link below as well. Enjoy cooking :)