Soak the black chana overnight or for at least 6~8 hours. Then cook them in lots of water until tender. I usually pressure cook for 3~4 whistles. Drain and keep ready.
Heat oil in a pan, add the mustard seeds. Once the seeds start to splutter, add the chickpea flour and cook for about 1 minute, stirring constantly, until it turns brown.
Add the kala chana, turmeric, chili powder, ground coriander and cumin, jaggery, tamarind paste, salt and 1~1½cups of water. Mix well and cook for 8~10 minutes, stirring occasionally.
Garnish with cilantro and Serve hot with rotlis.