In a mixing bowl, sieve the gram flour and rice flour. Now add the salt, asafoetida, red chili powder, and baking soda.
Add water little by little, as required. Using a spoon or whisk, mix the flour and water to prepare the batter.
The batter should neither be thick nor too thin. The consistency should be like dosa batter. In a kadai or frying pan, add the oil and heat over medium heat.
Prepare the brinjals
Cut the brinjal into thin round slices. You can cut the brinjals and directly dip them in the batter and fry. But I usually soak them in water for 10 to 15 minutes.
I read that soaking in water (I don't add salt, though) removes the bitterness of the eggplant. But I do it to remove the loose seeds and any worms or germs if present. But make sure to drain the water and pat them dry in a kitchen towel.
Prepare the bajji
When the oil is ready, dip the brinjal slice into the batter. Make sure both the sides are coated well and slowly drop them into the oil. You can fry 3 to 4 bajjis depending upon the frying pan size.
After 30 to 45 seconds, flip them. Fry them till they are golden brown on both sides over medium heat. Take the fried bajjis using a slotted spoon and place them on a paper towel to remove the excess oil. Similarly, make the bajji with remaining brinjal slices and batter in batches.
Serve hot with chutney or ketchup.
Notes
Soaking the brinjal is optional. If soaking, make sure you drain the water thoroughly and pat the brinjal slices dry.
Instead of brinjal, you can use potatoes, zucchini, or plantain. If using onion, carefully cut them into even and thin rounds.
The oil should not be super hot. Adjust the temperature as required while frying. If the oil is too hot, the bajji will brown up too fast, and if the oil is not hot, the bajji will absorb more oil.
The batter consistency is critical. If the batter is too thick, the veggies will be raw and unevenly cooked. If the batter is too thin, the coating will be difficult, and the bajji will absorb oil too. So add water as required. If the batter is too thin, add additional flour and salt to bring it to the desired consistency.