Take the required amount of dosa/idli batter. Add the tadka to it. Increase or decrease as per preference.
Give it a good mix until combined.
Heat a pan. I use a cast iron skillet. Once hot ( drops of water should sizzle), lower the flame, drop a ladle of the batter and spread it into a semi-thick crepe. Increase the flame to medium.
Add the onion and chillies (if using). Press it down for it to stick it to the batter.
Drizzle some oil all around the dosa. Let it cook for couple of minutes.
When browned, turn it over the other side.
Remove and set aside. Repeat with the rest of the batter.
Usually when I make it for breakfast, I add an egg per dosa for my boys. I whip an egg with a pinch of salt and pepper.
I drop a ladle of batter, spread it a bit and add the onion-chilli mix on top. Now on top of that, I add the whisked egg.
I spread it around with the help if the ladle.
Cover it with a pan to aid cooking of the egg while the bottom gets browned.
After couple of minutes, I remove the cover and flip the dosa.
Just needs few seconds on this side since its mostly done thanks to covering with a lid.
When done, remove and repeat with rest.