Rinse and soak the lentils for 6-7 hours or overnight. Make sure you use a large bowl to soak the lentils as they will double in size.
After the soak time is over, drain and rinse the lentils again.
Add the lentils to a food processor or blender, add 2 tablespoons water, and pulse into a fine paste.
Open the blender and scrape the lentils from the sides, add another tablespoon of water, and pulse again. Do not add all the water at once; add it in batches.
Pour just enough water to grind the dal into a thick yet fine paste. The batter should be thick and of dropping consistency.
Transfer the batter to a large mixing bowl and season it with cumin seeds and salt.
Whisk the Bhalla batter for about 5-6 minutes or until it is well aerated and double in size. You can use either a hand whisk, electric whisk, or a stand mixer to aerate the batter.
Take a small portion of the batter and drop it in a glass of water. If it floats on top, you are all set, but if it sinks, then you need to whisk for a few more minutes until you attain that texture. Perform the water test again and then proceed. Just remember the batter should FLOAT in water.