Wash Urad dal and soak for 2-3 hrs

Drain out the water from dal. Grind the dal to a fine paste in mixer adding little water as required

Transfer dal paste to a vessel and add 3 cups bansi rava to the same vessel. Add water little and mix properly. Let the batter ferment overnight

Add salt as per taste and baking soda to the batter in the morning. Mix in one direction, add water and bring to idli batter consistency. If you want, you can put tadka of rai, jeera, urad dal, chana dal, curry leaves. Mix well in one direction. Prepare idli from the batter.