It's thickened not with wheat or rice flour but with odiyal — flour ground from boiled, sun-dried palmyrah palm root, a starch found almost nowhere outside Jaffna's palmyrah country.
Prawns, crab, cuttlefish and fish are simmered with drumstick pods and tamarind into a thick, dark stew, bound with odiyal (palmyrah root flour) instead of ordinary starch. Roadside stalls and seaside carts around Jaffna ladle it out hot, especially in the evenings.