1. For the masala, put coriander leaves, garlic, green chillies, ginger and little water in a mixer jar and grind to a fine paste.
2. Heat a tablespoon oil in a non-stick pan, add mustard seeds and let them splutter. add asafoetida, curry leaves, masala paste and mix. add turmeric powder and cook for two minutes.
3. Add potatoes, salt and mix everything well. sprinkle some water, add coriander leaves and mix well. cover and cook for two to three minutes.
4. Transfer the potato mixture onto a plate and set aside to cool for ten to fifteen minutes.
5. For the batter, put gram flour, salt, red chilli powder, turmeric powder, coriander powder, cumin powder, asafoetida / hing in a bowl. add sufficient water and whisk well to make a semi thick batter without any lumps.
6. Add baking soda, mix well and set aside for ten minutes.
7. Heat sufficient oil in a kadai.
8. Divide the potato mixture into equal portions and roll into balls and press lightly.
9. Dip each ball in the batter, drain off excess batter and slide into the hot oil. deep-fry the vadas for four to five minutes on medium heat or till golden and crisp on the outside.
10. Drain on absorbent paper. arrange them on a serving platter and serve hot.