Trim the coriander and soak for 5 minutes in water. This removes all the grit.
Air dry the coriander leaves so that all the moisture is removed about 10 minutes. Pat dry if necessary.
Heat the oil in a small kadhai/wok and the urid dal till reddish add the hing/asafoetida and the switch off the gas. Add the chilli powder and let the mixture cool completely.
Transfer to the chutney bowl of the mixer/blender.
In the same kadhai/wok sauté the coriander leaves until the leaves shrink, (you can add the stalks toswitch off the gas and let the coriander to cool down.
By now your urid dal mixture must have cooled so grind a coarse powder.
Transfer the coriander leaves, salt and tamarind paste to the mixer and blend to a fine paste.
Sprinkle water if needed.
Store it in a clean dry container.
Notes
You can also fry the ground paste in oil. But do not fry for a long as the thokku may end up in bitter taste.
The amount of tamarind paste you will need will depend on the sourness of the tamarind.
You can also use red chillies in place of red chilli powder. If using add them to the heated oil first.