Rinse urad dal twice, then soak for 2 to 3 hours at least.
Then add it to wet grinder & grind it with very little water to a thick batter. Scrap the sides every now and then.
Grind it for at least 30mins. When you take a pinch of the batter and put it in water, it should float that’s the right consistency. The batter should be more like butter very smooth and light.
Now transfer the batter to a mixing bowl, add chopped onion, curry leaves and whole pepper. Mix well. Add required salt.
Now take a lemon sized ball, using your thumb finger make a small hole in the center like shown.
Heat oil, add the vadai into the oil. Similarly make other vadais too. As I used my small kadai I fried only 2 vadais at a time. Fry till golden.
Prepare all the vadais similarly and make it ready.
Now take 1/4 cup sambar in a bowl, add little hot water and dilute it.
Now add the prepared vadais into the diluted sambar, soak it for 2mins, then take it out and place it in the serving plate.
Now pour thick hot sambar over it.
Add chopped onion, sprinkle chopped coriander leaves.
Serve Sambar Vada hot!