For sambar, pressure cook toor dal with 1 & ½ cups of water for 4 whistles in medium flame. If your dal is hard to cook, recommend to soak ½ hour prior cooking.
Soak tamarind in hot water meanwhile for minimum 15 minutes. Extract tamarind juice with 1cup water.
Once dal is done, mash it well. Add turmeric, red chilli, finely chopped tomato, peeled small onion, slit green chillies, curry leaves, tamarind extract.
Pressure cook for a whistle.
In a kadai, splutter mustard and lower the flame or better switch off. Add sambar powder in the heat itself and quickly give it a stir.
Add the pressure cooked dal mixture to it immediately. Mix well and adjust water consistency.
You may have to add 1 & ½ cups water to 2 cups approximately.
Bring to boil and add coriander leaves, asafoetida powder, jaggery or sugar and top with ghee. Switch off the flame.
Now gently squeeze the excess water in the soaked vada, without changing its shape and arrange in the serving bowl.
Add hot sambar over it. Garnish with finely chopped onions before serving.