Wash dal and soak in about 3 cups of water for at least four hours.
Take the soaked dal and grind coarsely using very little water.
Add potatoes, cilantro, green chilli, ginger, cumin seeds, asafetida and salt to the batter of dal one after another and beat the batter for almost 2 to 3 minutes until it is light. Add water if necessary in order to soften the batter.
Ensure perfect consistency of the batter. It should neither be very soft nor very thick. Thick batter will make the vadas hard.
Add oil to the frying pan, at least 3cm deep. In order to ascertain whether or not the oil is ready put one drop of batter into the oil. If you see that the batter sizzle and comes up right away without changing color, the oil is ready and is at perfect temperature to fry the vadas.
Make small circular shapes out of the batter with the help of your hands or spoon and drop into the oil. Fry the vadas in small batches. Remember to fry them until they are golden brown.
The perfect vadas will have a crispy texture outside but will be soft inside.
Serve then with green chutney made from cilantro.
I tried it at home and it tastes really good. The recipe is great to be served as snack alongside your evening tea.