Soak urad daal and moong daal in 4 cups of water for 4-5 hours.
Drain and grind both daal, green chillies, ginger, cumin seeds, asafoetida & water in a grinder and grind to a coarse batter.
Take the batter in a big bowl.
Stir the batter briskly with spoon, whisk or spatula for a couple of minutes to incorporate air in it, this makes the batter light and fluffy.
We will now test the batter (whether it is ready to make vadas or not).
For this, will drop a small marble sized batter in a glass of water, if it comes on top then it means that the batter is ready to make vadas.
Heat oil in a kadai for deep frying the vada.
When the oil is medium hot, drop spoonfuls of the batter in the oil.
When the vadas become pale golden from the sides, turn them.
Fry the vadas till they become crisp and golden from all sides.
Drain on absorbent paper.
In a big bowl take water and mix 1 tbsp salt.
Add the hot vadas into the water and soak them for 15-20 minutes.
Take each vada and press between your palms to remove excess water.
Now place these vadas in the serving bowl.
Whisk the curd till smooth, pour it over the vadas.
Top them with the tamarind chutney. Sprinkle red chilli powder, roasted cumin powder, chaat masala and black salt on top.
Dahi vada is ready to be served.