Wash the urad dal ( skinless) and soak with water about an inch above the bean.
Wash and soak the bajra rava with water an inch above it too.
After about 2 hours the beans will be well soaked, grind the urad dal using the same water of soaking (and a bit excess if needed.)
The dal batter should be in a pouring consistency.
Drain the bajra rava and mix it well into the urad dal batter.
Add salt, mix well, put a loose lid and place the batter to ferment in a warm corner of the house.
Let this ferment for bout 6 to 8 hours till the batter turns fluffy and airy.
Once fermented, mix the batter and set it aside till the moulds are ready.
Prep the steamer with water.
Grese the idli moulds with oil
Pour the batter half way into each mould.
Place them in the steamer.
Steam for 15 minutes on a high steam.
Then lower the steam and continue for another 5 minutes.
Remove from heat after the time and let it stand for 10 minutes.
Unmould the idlies and they are ready to serve.