Grind it without adding water( as it’s already soaked) in a grinder in a way so that the mixture has thick consistency.Grind in a food processor if u have one.
Keep the mixture for 1/2hour or can add baking soda to make it soft.
Heat oil for frying in a voke or kadhai.
In a bowl take warm water and add some salt.
For making vada wet ur hands, take some vada mixture make hole in between with finger and drop in oil carefully.Likewise , make rest of the vadas.
Fry it on both sides till it become light brown ,take it out with spatula and drop in warm water.
Squeeze the vada to take out excess water and place it on another plate.
Method for making hot and sour chutney
Soak tamarind in warm water for 30min. then mash it and seive it .(store bought tamarind paste can also be used)
mix cumin powder , chili powder, sugar and salt according to your taste.Mix well.
Method for making yoghurt mixture
Beat the yogurt so that there are no lumps and add salt ,some cumin powder and chili powder.
Add soaked vada in yogurt and keep it covered for 1-2hour , if they are hard and if ur vadas are soft u can serve it cool after few minutes.
Serve vada with some yogurt mixture and garnish it with sweet sour chutney , cumin powder,chat masala, chili powder according to taste, u may also add green coriander chutney also.