Wash and soak rice in water for 2-3 hours. Drain and grind with salt to a slightly coarse batter, slightly thicker than Idli batter.
Pour the batter in a thick bottomed pan or a non-stick pan and cook and stir till it becomes like a soft paste.
Cool and shape into lime size balls and steam for 15 minutes.
For cockles gravy:
Wash the cockles, add enough water and boil till the shells open. Drain, cool and ease the meat out of the shells and wash again.
Heat 2 tsp of oil, add coriander and cumin seeds, pepper corns and fenugreek seeds. Roast till fragrant. Add chillies and coconut, fry till coconut is light brown. Cool and grind all these to a smooth paste.
Heat remaining oil. Fry onion till brown. Add the ground paste, fry for 1 minute. Add about 2 cups of water, cockles and salt. When cockles are cooked, drop in the rice dumplings, one at a time. Remove from fire after 1 minute.
Let the dumpling soak in the gravy for 1 hour before serving.