If you’re making this chaaru after having made polis, you will already have the cooking stock.
If not: pressure cook the jackfruit seeds for 4 whistles (or simmer them on stovetop until they are knife-tender). Once the seeds are cooked, drain the water—but save it for the chaaru.
If you’re making this chaaru after having made polis, you will also already have the poornam. If so, grind 4-5 cooked jackfruit seeds with 2T fresh coconut and green chillies. Add a little water if needed. Set aside.
If you do not have the poornams ready, grind 4-5 additional jackfruit seeds with 2T jaggery and 2T coconut into a smooth paste, adding a little water if needed. Set aside.
Soak the tamarind in 1 cup of water for 15 minutes. Mash well with your fingers to extract the pulp, and strain, reserving the tamarind water.
Transfer this to an eeya chombu or other pan, add the stock from cooking the jack seeds and water enough to make about 1 litre of liquid (if required), and bring to a boil until the raw tamarind smell disappears.
Add the turmeric powder and then crumble the poornam /the prepared sweet jackseed coconut mixture and the jackseed-coconut-chilli mixture into the simmering tamarind water.
Let this sit for a few minutes on a medium flame.
Next, add the rasam powder, and keep the chaaru on a simmer (do not boil) until it becomes somewhat frothy.