Cut the coriander with salt. Soak it in water for 10 minutes. Squeeze and take it out.
To a blender jar add coriander leaves and tamarind paste. If you are using tamarind, soak a small lemon sized in water for 20 minutes. Squeeze and take out the extract.
Grind the coriander and tamarind to a smooth paste
Heat oil in a pan, add mustard seeds. When it splutters add turmeric powder and chilli powder.
Saute for few seconds and add the coriander tamarind paste. Mix well and cook on low flame for 1 minute
Now add the asafoetida and salt, mix well and continue to cook for few minutes.
When you see the thokku thickening, add the fenugreek powder and jaggery. Mix well and continue to cook for another 3 minutes and you will see the oil coming out at the edges. Switch off the fire. Let it cool completely. This will look like a slurry at this stage. When it is completely cool, transfer it to a glass bottle and refrigerate till use