In a mixture jar, add moong dal and urad dal. Grind it into fine powder and sieve grinded flour.
Now add water gradually and soak flour for 25 minutes.
Add 1-2 tablespoon water and whisk batter for 6-7 minutes till it changes its color and become light and fluffy.
Then add salt, cumin seeds, green chilli paste and ginger paste. Mix well.
Now add baking soda and mix well with batter. prepare a medium thick batter.
now with a wet spoon or using hand, drop a spoonful of batter into the hot oil.
keeping the flame on medium, stir occasionally. fry until the vada turns golden brown and crisp.
drain off the vada with wire rack to remove excess oil.
now in a large bowl take 5-6 cup of slightly hot water. add ½ tsp salt and ¼ tsp hing. mix well making sure it is well combined.
now drop the hot fried vada into the water and dip completely.
soak for 45 min to 1 hrs, or until the vada absorbs water.
then squeeze off the water and transfer it to the plate.