Slice the onions thinly and take them in a mixing bowl. Also, add chopped green chillies.
If you do not have green chillies, then add red chilli powder. You can also add chopped coriander leaves if you want.
Add the spices - carom seeds, turmeric powder, asafoetida and salt.
Mix everything well. Cover and keep the onion, chillies and spice mixture aside for 15 to 20 minutes.
The onions would release water and then you can addwater as required in the batter.
Add gram flour (besan). If you plan to add baking soda, then add at this step.
Add the required amount of water to make medium-thick batter.
Stir the whole mixture very well with a spoon or with your hands. The batter is ready to be fried.