Put onions,
garlic, ginger and chili powder into blender container and blend to a
smooth paste.
Add a
tablespoon of thin coconut milk if necessary.
Scrape the
blended mixture into a saucepan, wash out blender with the thin coconut
milk and add to saucepan together with the ground spices, lemon rind and
curry leaves.
Bring to the
boil.
Reduce heat and
simmer for about 8 minutes.
Then add the
fish, tamarind liquid and salt and simmer for 5 minutes.
Add thick
coconut milk and stir until curry reaches simmering point once more.