Sri Lankan Fish Curry

This relatively mild, lightly sour, and deeply aromatic yellow curry, adapted from Yusra and Mohamed Ali Makim, is a breakfast staple eaten throughout Sri Lanka. Goraka, or Garcinia cambogia, a dried tropical fruit available at specialty spice shops and online, gives the mixture its characteristic sweet-sour flavor. If you can't find it, rehydrated and deseeded tamarind pulp makes a good substitute. Use as thick a coconut milk as you can find.