In a heated pan, cook the chopped potatoes, peas, ginger, onion and green chillies in the water. When it starts to boil, add salt.
Let it continue cooking until the mixture has been reduced to 1/4 the pan. Lower heat to warm and add the coconut milk, curry leaves and the butter.
When it reaches a boil again, remove from heat.
Serve warm with appams, rice or dosas.