Prepare the clams: Wash the clams under running water thoroughly 2-3 times. Place the clams in a big vessel. Cover it with the lid and place on medium flame. Do not add water at all. Partially remove the lid after 3 minutes.
Check the clams after another 2 minutes. They must be open now. Toss the clams so that the clams in the bottom come up. Turn off the flame if all the clams are open. Let this cool completely.
Gravy preparation: Char roast 2 onions, garlic head and the coconut halves on the gas burner. In a small pan roast the spices and the ginger in 1 tsp of oil.
Grate the roasted coconut. Peel off the outer layer of the onions and the garlic. Use only 7-8 cloves of the garlic. Rest you can use for any other preparation. Cut the onion in rough chunks.
Grind the coconut, onions, garlic and the ginger and spices, turmeric and malvani masala finely.
By this time the clams will be completely cool. Sort the clams by separating the empty clam shells. Take the clam shells which has the meat in it. Throw away the empty ones. Throw away the closed. Do not throw away the liquid in the vessel.
Once the clams are sorted strain the liquid through a muslin cloth as it may contain small grains of sand from the clams.
Now heat the oil in a big kadai so you can easily stir the clams. Add the potatoes now if you are using them. Add the ground paste to it. Stir for a couple of minutes.
Add the clam strained clam juices to this. Cover and cook till the potatoes are done.
If not using the potatoes, then add the clams once you add the clam juices. Add the kokum. Cook for 5-7 minutes. Turn of the flame and serve hot with chapati or rice. These taste much better the next day.