Start by soaking the white lentils for 4 to 8 hours to ensure maximum hydration so you end up with a light fluffy and crisp vada.
Using a strainer, strain all the excess water from the urad dal and set aside.
Blend the dal along with the ginger either in a food processor or high-speed blender, adding water if required, into a very smooth batter that is thick yet pourable. Make sure to add very little water while blending the dal. Transfer to a bowl.
Add the salt followed by chopped onions, cumin seeds, crushed black peppercorn, green chilis, curry leaves, coconut pieces, and chopped coriander. Stir well to combine all the ingredients into a smooth and consistent batter.
Cover the vada batter and allow to rest in a warm place while you preheat the oil.
This resting process will allow the batter to rise and fluff a little, ensuring light and crispy vadas.
Preheat the oil to 350° F. Use a medu vada maker to get the traditional medu vada shape.
Traditionally, the medu vada is scooped into the palm with four fingers and an indent made in the center with the thumb before dropping it in the hot oil.