Wash and soak the urad dal in four cups of water overnight or for 7-8 hours. Drain off the excess water the following day. Grind dal to a smooth paste by adding 2tbsp of water if required.Add salt, black pepper powder, raisins, chopped ginger and asafoetida into the batter and mix the batter for 10 minutes in one direction.
Heat sufficient oil in a kadhai,Drop batter in teaspoonfuls in it and fry until on medium flame till it become light golden and then take it out.
Put vadas in sufficient amount of hot water and leave it aside for 10 minutes.
Squeeze vadas between your palms to drain out the water. Whisk the yoghurt, add sugar, salt, black salt into it, mix it well.
Take a serving plate, place vadas on it, then pour whisked yoghurt over it, sprinkle roasted cumin and red chilli powder and chat masala over it. Garnish it with some raisins and serve it.