Rinse urad dal under running water. Then soak it in 3 cups of water for 5 to 6 hours. Once soaked, drain all the water.
Add the soaked urad dal to a grinder jar. Add 2 to 3 tablespoons ice-cold water or as required. Grind it till the batter looks fluffy and thick.
Transfer to a large bowl. Whip the batter for 2 minutes on medium speed. This process is very important. It will create aeration and will help you get the fluffy, soft, and light vadas.
Take out the batter into a wide bowl. Add onion, cilantro, green chilies, curry leaves, ginger, coarsely crushed black pepper, and salt. Mix everything well.
Dip your hand into the water and wet the backside of the steel bowl. Place some batter on it. Dip your index finger in water, and make a hole in the center.