Pressure cook the potatoes for 2-3 whistles. Heat a pan with oil and add the mustard,urad dal, chopped ginger, green chillies, curry leaves and chopped onions. Fry for a minute and then add the spice powders and salt. Crush the potatoes slightly and add it to the masala. Mix everything well and add the chopped coriander leaves at the end. Potato Masala is ready.