Clean and cut the pomfret.
Grind the mustard seeds and turmeric.
Slice the onions fine. Grind ginger and garlic. Slit the chilies.
In a saucepan heat the oil and fry the ground mustard seeds and turmeric slightly, then add the ground ginger and garlic and fry for a few seconds.
Now add the green chilies and fry till brown.
Add the onions and fry till tender.
Sprinkle with a little water now and then, to mellow the mustard smell.
Add the thin coconut milk (second extraction) and stir constantly to prevent curdling.
Add vinegar and salt. Let it boil for a while.
Add fish and a little later the thick coconut milk.
Cook till the fish is done, stirring to prevent curdling.
Remove from heat and garnish with chopped coriander leaves.
Serve with boiled rice.
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