Clean the clams thoroughly under running water. If the shells are tightly shut, the best way to open it is to leave the clams in the freezer for about 30 minutes. Bring to room temperature and place in warm water for another 15-20 minutes. Most clams open up after this time; any tightly shut ones should be discarded.
Open each clam shell and scoop the entire contents into one shell and discard the other. (This is an easy task but if you do not have enough time, get your fishmonger to do the job for you).
In a non stick plan, dry roast the grated coconut and onions till the raw smell has gone off and the coconut has taken on a light brown colour. Make sure that you do not burn or else the dish will taste bitter.
Next, add the spice powders, mix well and sauté on low heat for another 30 seconds. Cool the mixture.
Grind this mixture along with the garlic, ginger and tamarind paste adding just a little water. The ground mixture must be coarse in consistency.
In another pan, heat oil and crackle mustard seeds. Then add the curry leaves and sliced onions; sauté till the onions turn light brown.
Then add the ground masala and fry lightly on low heat for about 2minutes.
Add the clams and season with salt. Remember that clams tend to be on the saltier side so be careful.
Cook on low heat covered for a couple of minutes; add a bit of water if too dry. Clams cook relatively fast so keep an eye on the dish.