Wash properly and soak the Urad dal in water for six hours.
Drain the water and grind the urad dal properly so that it becomes light and fluffy, take out in a mixing bowl,add a little salt and asafoetida powder and mix well.
Heat oil in a kadhai and when it becomes hot then take the dal batter in form of small balls between the fingers and drop smoothly in the oil. Fry till the wada becomes golden brown.
Drain the wada and put them in cold water for few minutes. take out from water and squeeze a little between the palms (to remove excess water)
Put the wada in serving bowl and cover with cold yogurt.