firstly, soak 1 cup urad dal for 5 hours.
drain off the water and transfer to the mixi or grinder. also, add 1 chilli and 1 inch ginger.
blend to smooth paste adding water as required. try to add a minimal amount of water to prevent the batter from turning watery.
transfer the urad dal batter to a large bowl.
take ¼ cup soaked moong dal into the blender.
blend to smooth paste and transfer to the same bowl of urad dal batter.
now add 1 tsp salt and mix well using the whisk.
prepare a thick batter. if the batter is runny then add a tbsp of rice flour.
now wit 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 over kitchen paper to remove excess oil.
now in a large bowl take 5 cup 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 30 minutes, or until the vada absorbs water.
after 30 minutes, squeeze off the water and transfer to plate.