The colocasia leaves with stem look like this. This is the picture taken at my mother's place in India.
Wash the stems under running water and peel the skin off. Chop them in to medium sized pieces.
Method
Soak tamarind in 1/2 cup of water for about 15 minutes. Heat a pan adding all the seasoning ingredients in the order mentioned. As the mustard seeds sizzle, include chopped stem.
Saute the stem for about a minute, then add tamarind extracted juice. Discard the residue of tamarind. Add salt, jaggery and rasam powder. Let it boil for few minutes. Switch it off.
Mouth sizzling tasty colocasia stem kayirasa is ready to serve with steamed rice.
Notes
Choose the colocasia which has no itching characteristic. Some tend to itch the throat and tongue.
The stem takes very less time to cook, so do not saute for longer.
If overcooked, the stem doesn't taste good, so let it be crunchy.
Balance sweet and sourness for the perfect tasting kayirasa.