Soak black gram for at least 2 hours.
Grind it into a thick fine paste by adding ginger, salt and required quantity of water.
:- The batter should be thick so that we can easily make vada out of it.
Mix baking soda with the vada batter.
Heat oil in a heavy bottom pan.
Roll out small lemon sized balls/vada out of the batter and deep fry it in oil.
When vada turns golden brown, take it out of the oil and drain it on tissue paper.
Make sugar powder out of 1 cup sugar.
Beat the curd by adding powdered sugar.
Transfer this curd into a large serving dish and dip the fried vadas in it.
Heat 2 tbsp of oil in a pan and splutter mustard seeds.
Add curry leaves and when it becomes crispy.
Add whole red chillies and remove from fire.
Sprinkle this over dahi vada and keep it in the fridge (not in the freezer) for half an hour (so that the vada gets soaked in curd).
:- Dahi vada is ready to serve.