Now grind the dals in a blender without adding much water. After you initially grind the dals, you will get a powdery consistency. Add a teaspoon of water and blend again.
Making the Masala Vada Batter is slightly painstaking as adding a lot of water will make the batter runny and vadas cannot be formed with proper shape.
Keep mixing the batter inside the blender so that the entire lot blends thoroughly. It is alright to leave it slightly coarse as this would give a nice texture to the Vadas.
Once the batter is ready, take it out on a large bowl. Add the fennel seeds, asafoetida, salt and the finely chopped onions. Add the fistful of soaked dal that you had kept aside earlier.
Remember, the onions tend to give away water into the batter. So add the onions when you are ready to fry the vadas.
To make the vadas, first heat the oil to fry the vadas. Roughly one third of your kadhai should be full of oil. To check if the oil is heated enough, drop a small part of the batter in the oil. If it rises immediately to the surface, then the oil is hot enough.
Now, take batter about the size of a lemon. Grease your left palm and pat the batter into a round shape. Once the batter is in a round shape, take it in your right hand, hold it lightly with you right hand fingertips and gently lower into the oil. Make sure the flame is at minimum. Be very careful about the hot oil splashing on your fingers. Depending on how much oil is there in the pan, you can add no more than three vadas at a time.
Let the vadas cook for a bit before turning them over with a frying spoon. Cook well on both sides. You would notice the onions on the surface have gone dark and the vadas have turned golden brown.
Take the vadas out on a filtering pan, or put them on a tissue paper to get rid of the excess oil.
Masala Vadas are now ready! Have them with onion or coconut chutney.