Season the fish pieces with salt, pepper and a drizzle of oil. Keep for 15 minutes and then shallow fry the fish. Place skin side down first to get it crispy and golden; then turn over and cook till almost done. If using a small pan, fry the fish in batches and keep aside.
Add the soaked chillies and garlic to a food processor and blend to a fine paste (add a little water if necessary).
Once the fish pieces are cooked, reserve about 2 tbsp oil and drain or wipe off the excess oil. Place on low heat and add the shrimp paste; mash with the back of a spatula and cook till it gets toasty. Then add the chilli garlic paste and continue to cook, stirring frequently, till fragrant.
Add the jaggery (or gula Melaka/palm sugar) and continue to cook till dark and glossy. Slowly add the tamarind puree, one tbsp at a time. After adding the first tbsp, mix well and taste. Add more as necessary. Keep tasting and adjust tamarind and jaggery to get the desired flavours of spicy, sweet and tangy.
Once the desired balance has been achieved, add the fried fish pieces, season with salt if necessary and toss gently,