1 cup white urad daal (lentil) soaked overnight
1 small piece ginger
1 green chilli (optional)
a small pinch of cumin seeds
Grind the daal  (lentil) with a little water with the ginger, green chillies. Grind it into a smooth thick batter. Add salt to taste and cumin seeds and leave it covered for a few hours to ferment.
FILLING:
1-2 potatoes boiled and mashed
1 small onion chopped very fine
2-3 tablespoons of green chutney (for the green chutney grind green chillies, ginger, garlic, and a little coriander leaves to a paste with lemon juice)
salt to taste
1 teaspoon of chaat masala
mix the mashed potatoes with the above ingredients and shape into balls.
TO SERVE:
1 bowl white yogurt , beaten , add a pinch of salt and a bit of sugar and some chaat masala
coriander leaves chopped fine
Tamarind chutney (you can buy it ready made or make it at home)
red chilli powder
TO MAKE THE VADAS
heat oil in a deep fryer. dip the potato balls in the ground daal batter and coat. put into the hot oil and fry till crispy.
cut them in half when slightly cooled and drizzle the yogurt and the tamarind chutney over them.
sprinkle with red chilli powder
SERVE IMMEDIATELY!!