Heat two tablespoons ghee in a pan, add cumin seeds and green chillies.
When the cumin seeds change colour, add potatoes, crushed black peppercorns, coriander leaves and rock salt and mix well.
Allow the mixture to cool. Divide the mixture into lemon sized balls, keep aside. Make a thick batter using waterchestnut flour and water.
Add rock salt to taste. Heat sufficient ghee in a kadai, dip the vadas in the batter and deep fry.
Drain onto an absorbent paper. Serve hot with coriander and coconut chutney.