Wash and clean fish pieces. Wash till you get a clear water and finally add rock salt (kalluppu) and wash again. Drain out water thoroughly and wipe each fish piece with a kitchen towel. In a wide bowl, marinate fish pieces with 1/4 tsp turmeric powder and 1/2 salt. Cover and keep aside for half an hour.
Heat oil in a meen chatty (preferably earthen pot) or pan. Add finely sliced small onion / shallots / chuvannulli. Fry on a medium heat till golden colour.
Add sliced garlic, ginger, slit green chilli and curry leaves and fry till crisp and golden colour.
Add diluted spice paste and stir on a low heat for 2 - 4 minutes or until the raw smell goes and water dries up.
Add kudampuli along with strained water (reserved 2 tbsp water, in which kudampuli soaked) salt to taste and 1/2 cup water (100 - 125 ml).
Stir all the ingredients well.
Cover with a lid and cook on a low to medium heat for 5 - 7 minutes or until it boils.
At this stage, add marinated fish pieces gently (level of the water should be equal to fish pieces. It should not be 1/2 to 1 1/2 inch above fish pieces. Fish curry won't be tasty if the gravy is too thin. Here final adjustment of the gravy is with thick coconut milk).
Cover with a tight lid and cook on a medium to low heat for 8 - 10 minutes or until done / fish pieces well-cooked / gravy slightly thickens cooking time depending upon the variety of fish). Switch off the heat .
Sprinkle uluva podi.
Now add 75 - 100 ml thick coconut milk and gently mix well. Serve with rice / boiled tapioca / appam.
Allow the curry to stand for at least 2 hours before serving so that the gravy and fish absorbs all the flavours.