Soak urad dal for 2 hour at least. (Use whole urad dal without skin(muzhu ulundu)for better result).
Grind urad dal with only little water till fluffy. Please note the following points:
Add urad dal little by little(no water),while the grinder is running.
b)Just sprinkle water now and then to avoid jamming of the grinder. Using ice cold water is recommended.
c)Stand near till you finish grinding for sprinkling water now and then and wipe the urad dal that sticks to the wall of the grinder container.
d)This whole process takes around 12-15 minutes,you will get a fluffy white batter.
Now chop onions,ginger,green chillies,coriander and curry leaves and add all these to the batter along with salt and asafetida.(You can add ginger and green chillies while you are grinding the batter itself,if you don’t want to come in mouth.If you decide so,first add ginger and chilles,then urad dal)
Now mix well,keep aside and heat enough oil in kadai (be generous or else vadas may stick to the bottom and get burnt).
Now wet your right hand well and make a small ball.
And use ur thumb to make hole in the middle.
and drop it in oil,(just invert the vadais over the oil and slightly shake ur fingers)
Fry in medium flame,turn the vadais and fry till both the sides turn crisp and golden brown.