Wash and soak the chana dal in lots of water for 5-6 hours.
Drain well and grind to a coarse paste, without adding any extra water.
Add all the remaining ingredients to the paste, mix well.
Keep the oil to heat in a deep heavy bottomed pan / kadai.
Once the oil is hot, you can test by dropping in a small round of dal mix into the oil. It should immediately sizzle, go to the bottom of the kadai, and come straight up to the surface.
On a greased palm or a cling film, pat vadais of around 1.5" diameter and 1/2 inch thickness. As you form each vadai shape drop it along the sides into hot oil.
Allow this to fry on medium heat, for around 4 minutes or so on one side. Once the bottom side turns golden and crisp, you can flip it around and similar fry this side for 3 minutes or so.
Drain on a colander covered with a few layers of kitchen paper / tissues to absorb the excess oil.