soak the urad dal in enough water for 2 hours.
drain the water from the urad dal and keep it aside. we will use some of this water for grinding the idli batter in grinder as it helps in good fermentation.
take the urad dal in the wet grinder / mixer. add some of the urad dal strained water and begun to grind.
if the batter appears too thick, add some water.
grind to a smooth, fluffy batter for atleast 20-25 minutes.
pour in a deep pot.
steam the rava without mixing water to rava in a steamer for 20-25 minutes keeping in a medium flame.
mix the steamed rava to the batter well.
add salt and mix well.
make sure to give some space for fermentation and rising of the batter.
cover and ferment in a warm place for 12 hours.
you can see the batter has raised almost double indicating its well fermented.