Soak the tamarind in water for some time, extract the juice and keep it aside.
In a heavy bottomed pan, heat the ghee and add the sundakaai vathal and fry for some time. Take this fried vathal aside.
Now heat the oil in the pan, and add the mustard seeds. When the mustard seeds starts to sputter, add vendhayam (fenugreek seeds) and omam and fry till the vendhayam (fenugreek seeds) turns golden brown colour.
To this add the sambar powder and fry for a while.
Now add the tamarind extract and salt and let the kuzhambu boil in medium flame till the raw smell goes off.
In a bowl, add the rice flour and little water and make it dissolve in water.
Add this rice flour water in the Boiled kuzhambu and stir it well to avoid lumps.
When the kuzhambu starts to boil, add the fried sundakaai vathal, stir it and switch off the flame.
Now the mouth-watering vendhaya kuzhambu is ready to serve with hot rice along with a spoon of gingili oil.