Soak urad dal and yellow moong dal overnight.
Grind it in a mixer with 1 or 2 tbsp of water. Use as much less water as possible.
Keep it aside for 4 hours. This is needed as it will ferment the batter and make the wadas light.
Spoon the batter directly into the hot oil. Fry the wadas till golden brown on a medium heat.
Once fried keep the wadas on paper towel for 1 minute to soak excess oil.
In a separate pot boil about 1 liter of water. Add 1 Tbsp salt. Add the fried wadas into the hot water. The wadas need to be kept in boiling water as it will remove the excess oil.
Remove the wadas after 10-15 minutes. Keep them on a paper towel for 5 minutes to remove the excess water.
In a separate pot mix yogurt and sugar. Whisk the mixture until all the sugar gets dissolved.
Arrange the wadas in a bowl and pour yogurt mixture on it. Keep it in the fridge for at least 2 hours or until the wadas absorbs the yogurt.
While serving the dahi wada garnish it with coriander powder, cumin powder and red chili powder.