Rinse and soak urad dal for 6hrs.
Soak idly rava for 6 hrs.
Take dal in a blender or add full dal to the wet grinder and blend it smoothly by adding little by little water when ever it required.
Transfer the batter to the large vessel and add salt.
Drain off the water and also squeeze the excess water from the rava with hands and keep aside. Make sure that there is no water in the rava.
Add idly rava to the urad dal batter.
Mix the rava and urad dal batter nicely.
Keep the batter in a warm place and let it rest for 6-8 hrs or until it ferments well without becoming sour. If you are living in a cool place, place the batter in the oven and turn on the light.
A well fermented batter rises well and looks fluffy.