Grind coconut with onion and keep it ready
In deep large pan /kadai, add oil, mustard seed to splutter ,add curry leaves .Add the garlic fry for few seconds then add the finely chopped onion and saute till it turns transparent color.
Add the finely chopped tomato ,once tomato is mashed up add the coriander powder ,chilli powder ,turmeric powder and sambar powder along with required salt and saute for few more minutes.
Once the masala saute well ,add tamarind juice followed by coconut onion grinded past . Mix everything well and allow it to cook for 4 to 6 minute .
After started to boiling the kuzhambu , slow down the flame and carefully drop the boiled urundai one by one.
In medium flame allow it to cook for 6 to 10 minutes.The kuzhambu has to soak with urundai . Don't stir or mix the urundai during this stage .Once the urundai soaked with kuzhambu .Switch off the flame and the Paruppu Urundai kuzhambu is ready.