Wash rice and urad dal separately 2-3 times then Soak rice and urad dal in water for 6-8 hours. Drain all the water from the urad dal and grind it to a fine paste. Add water accordingly.
Grind the rice to a coarse paste (add water as needed) and then mix both the pastes together in a large bowl and whisk them well. Make sure that the consistency is thick.
Now, the idli batter needs to be well-fermented. This step is very important to get soft and fluffy idlis. Keep the batter in a warm place to ferment. Once the batter has risen, add salt and eno to it and whisk to mix it well.
Grease the idli stand with oil and take a full spoon of batter and fill the idli mould. Add 1 cup of water in the idli steamer and let it boil. Put the idli stand inside and close the lid. Let the steam build for 15-18 minutes before turning off the stove.
If you are using a cooker, use it without a whistle and steam it for 15 -18 minutes and then switch the stove off. In both cases, wait till the steam is released before you take the idli to stand out. Wait for another 5 minutes and then use a sharp knife/spoon to scoop the idlis out. Serve warm with coconut chutney.