Wash and soak both lentils for 4 hours.
After 4 hours, discard the water and add to a blender jar.
Grind to a fine paste. add water as required.
Transfer to a vessel. Add salt.
Mix properly. Cover and allow to ferment overnight in a hot place
Next day, if required add some water to adjust the consistency of the batter.
For making Idli, fill water in a pan or Idli cooker and let it boil.
In the meantime, grease idli moulds and pour about 2 tbsp of the batter in Idli mould.
Put the mould in the Idli cooker.
Cover and steam for about 12 minutes.
If for some reason, the batter has not fermented well, then you may add Eno. Please note that after adding Eno, pour the batter immediately into the Idli mould.
Serve hot idlis with any chutney of your choice.
The idlis can be refrigerated or even frozen. Whenever you want to have them, sprinkle some water, cover and microwave for a minute. They will turn soft.