Wash cilantro and pat it dry. Remove the hard and stiff stems.
Place the clean cilantro under the sun and let it dry for one to two hours. You can dry it in the shade too. Just make sure there isn't any moisture.
Heat a pan or kadai and when it is hot, add the chana dal and roast until it turns deep golden brown. Transfer it to a mixer jar.
In the same kadai, add the urad dal and roast until it turns light brown. Then add the asafoetida and dried red chilies and roast until the chilies are crisp and urad is deep golden brown.
Transfer the urad to a mixer jar, and in the same pan, add the tamarind piece and roast for 30 seconds and turn off the heat. Let it sit in the residual heat.
Let the lentils cool. Add salt and the tamarind to the mixer jar.
First grind the lentils and red chilies. Mix coarsely like below.
Now add the dried cilantro.
After adding the cilantro, use the pulse mode and grind them. Do not grind the ingredients continuously, or it will become a thick blob. Use a spatula to mix the ingredients as required.
Pulse at regular intervals until you get a nice coarse and dry powder, as shown below. Let it cool a bit and store it in an air-tight container.
Adjust the salt and red chilies as per your preference.
Make sure there isn't any moisture in the cilantro. We want it completely dry. Dry cilantro ensures a longer shelf-life.
Also, for this recipe, I recommend tamarind flesh/pods, not the paste. Tamarind paste will make the chutney wet, and the consistency won't be like a dry spice powder. It will be slightly wet and more like thokku. You can try that way as well but make sure to refrigerate.
After adding cilantro, use the pulse mode and blend the spice mix. Do not blend it continuously.