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 use in making chaaru later. Also set aside about 6-8 seeds for the chaaru.
Peel the jackfruit seeds if you haven't already--their white seed coat is papery and inedible.
Grind the remaining seeds with the jaggery and coconut into a smooth paste. If you were making this with chana dal, you’d need no water. With jack seeds, you’ll need water, but use just enough to allow this to become a smooth paste.
Transfer the paste to a heavy-bottomed pan, set on medium heat. Cook this until it is almost completely solidified.
Add the powdered cardamom and the nutmeg
To make barfi: press this hot filling into a small, well-greased pan or plate, allow to cool, and cut into squares. Garnish with fresh coconut and serve warm.
Or, continue with the poornam: Once the mixture is cool enough to handle, form into large lime-sized balls. Set aside.
Remember to reserve 1-2 poornam balls for oliga chaaru, to be made next.