Soak urad dal in a separate bowl. Wash and soak rice + cholam in another bowl. Let it soak for 3 hours.
First grind urad dal with ice water (add little by little) to a fluffy batter. Collect the batter in mixing vessel.
Next grind rice + cholam with salt until smooth. Add water carefully. Do not make runny batter. Mix both batter and keep aside for 2-3 hours. I keep in fridge later until use.
To make paniyaram, I keep the batter outside for 1 hour. Take just half the amount of batter.
Temper in a kadai with oil. Mustard, urad dal followed by finely chopped chilli and chopped onion.
Fry until onion turns translucent. Add to the batter.In goes finely chopped coriander leaves. Mix well.
Heat a paniyaram pan/ appe pan with little oil. Fill with batter.
Cook covered in medium flame for 2 mins or until golden. Flip and cook for one more minute or until its golden. Remove in a plate to serve.