Wash and soak urad dal overnight.
Place the urad dal in a sieve to completely drain all the water
Add it to a mixer grinder, add a tablespoon of water at a time (I used between 4-6 tablespoon water), and grind it to a smooth paste. You may need a little less or a little more water, but try to use as little water as possible. This entire process can take up to 6-8 minutes. It's important to keep mixing it with a spatula and grinding.
Mix salt and hing in the ground urad dal and set it aside for ten minutes. The hing acts as baking soda and helps make the batter lighter.
Place the oil in a kadhai for heating while you whisk the batter
Use a hand whisk to whisk the ground urad dal until it's light and fluffy - approximately 5 minutes. You’ll feel the batter becoming airy and fluffier and also getting lighter in colour from a yellow to pale white.
To make vadas, wet the back of a flat katori with water. Take a lime-sized amount of batter in your dominant hand (in my case, my right hand) and place it on the wet surface of the katori.
Using the fingers of the dominant hand, gently tap to press it into a flat circle. Gently drop the vada in hot oil by turning the katori over the kadhai (close to the oil so the vada doesn't splash into it) and moving the fingers slightly so the vada slides into the oil. Alternatively, the same can be done using the palm of your subservient hand instead of the katori.
You should see it start to puff up slightly. Cook it on a medium flame for 2-3 minutes till golden brown on both sides. Remove the vadas using a skimmer and keep aside on a tissue lined plate. Repeat with the rest of the batter.
Add 2-3 cups of hot water into a bowl and combine it with 1 teaspoon of salt.Soak the fried vadas in it for 20 minutes.
Once soaked, remove each vada one-by-one and squeeze it well enough to remove as much water as possible.