Wash dhule urad dal in water till water comes clean. Soak it overnight or at least 4 hours.
When you are ready to make vadas drain the water from dal. Grind it to a smooth, thick paste. Add very little water if needed.
Add soda (optional) and beat the dal till it becomes fluffy.
To check if batter is ready for frying drop small amount of batter in water and it should float. This means vadas are ready for frying.
Heat some oil in kadai/wok/pan at medium heat. Drop small balls of batter either with hands or spoon in oil.
Deep fry them till they are golden brown from both the sides.Now take warm water in a big bowl and keep it aside.
Heat a small pan at medium heat and add ½ tsp of hing (asafetida) in it. Add this hing tadka and salt in water.
Now dip the vadas in water for at least 15-20 minutes. In the meanwhile beat the curd in a bowl. Add sugar and salt to it.
After 20 minutes or when you see vadas are soft enough take them out of the water, squeeze the water out and put the vadas immediately in the curd. Let them stay in curd for few minutes.
Now take them out in a serving plate and add more curd to them.
Garnish them with sweet chutney, coriander chutney, red chilly power, roasted cumin powder and some salt.