Soak both the rice and the urad dal, separately, in water for 4 to 5 hours. Drain and rinse the rice and dal. Add water to the rice and grind it to a smooth paste. Add this rice batter to a large bowl.

Grind dal to make a thick and smooth paste. Add the dal paste to the rice batter. Now add coconut milk to this batter and whisk well to make a lump free batter. Add Salt and 2 tsp Sugar to this batter and whisk well. Keep aside.

To make yeast solution, mix the yeast in warm water. Stir well and let it rise for about 10 minutes. Add this yeast solution to the prepared batter and stir well. Cover the bowl and keep aside to ferment for about 2 hours or till it doubles in quantity.

Heat water in a Steamer. Grease the idli moulds. Spoon the batter in each mould and place it in the steamer and cover and steam the sannas for about 15 minutes or till done. Insert a toothpick to check if it is cooked. If the toothpick comes out clean means it is done. If not, then steam for few more minutes.

Allow the idlis to cool down. Run a knife all around the idlis and they will pop out of their moulds. Soft, fluffy and spongy sannas are ready. Serve hot with curry or chutney of your choice.