Add the chopped garlic, chillies and ginger in a pestle motor and ground it into paste.
Heat oil in pan on medium heat. when hot temper with mustard seeds and curry leaves and hing.
When it crackles add in the ginger-garlic chilli paste and saute for a minute stirring continuously.
Then add the boiled potatoes along with turmeric and salt and mix it well with the spices.
Cook for 2-3 minutes. then add chopped coriander leaves and mix it well with the potatoes.
Take it off the heat and keep it aside. When cool to handle make small equal sized balls and keep it aside.
Heat enough oil to deep fry the vadas in a deep frying pan.
Meanwhile in a large bowl add the all the ingredients listed under batter except for the oil. Add water little by little to make a semi thick batter.
Add one tsp of hot oil to the batter and mix it well.
When the oil is hot, dip the potato ball in the batter and drop it slowly in the oil.
Deep fry the vadas until golden and crispy evenly. Remove it on an kitchen towel.. Repeat the process for the remaining vada’s.