Soak rice and urad dal separately for 3-4 hours.
Grind urad dal until light and fluffy. Grind rice to a slightly coarse paste.
Mix both the batter together and add salt as per taste. The consistency of the batter should neither be thin nor thick, you can adjust by adding small amount of water.
Keep the batter in a warm place for 6-7 hours or overnight depending on season to ferment. In summers it takes lesser time to ferment as compared to winters.
When batter is fermented keep it aside and prepare seasoning for the batter.
Heat oil in a kadahi and add mustard seeds, cumin when these start to splutter add ginger powder, asafoetida, and coriander leaves.
switch off the heat and add this seasoning to batter.
Now brush the wooden bowls with oil and pour the batter in these bowl so these are half filled.
Steam these bowls in Steamer for 12-15 minutes and then allow the steamer to cool a bit before taking them oit.
In the meanwhile you can prepare another tempering of ghee, chana dal, curry leaves , mustard seeds and pour small amount on each idli.