Boil the potatoes and peas.
Cut half the potatoes into big pieces and mash the other half.
Then grind onions, chillies and ginger with little water to make a fine paste.
Heat the oil, add mustard seeds, cumin seeds and fry till they pop up.
Add the fine paste and fry for few minutes.
Add the tomatoes, salt, turmeric powder, red chilli powder, garam masala and mix well.
Then add the boiled potatoes, peas, one cup of water.
Cover and cook for few minutes.
Add the beaten curd and cook on slow flame until a thick gravy is formed.
Garnish with corainder leaves.