Heat oil in a pressure cooker. Saute onions and green chillies till wilted.
Add the ginger garlic paste and saute for a minute.
Add the masala powders and cook for a minute.
Add the tomato and a dash of water and cook till tomatoes are all mashed up.
Add the potato and coat well. Add around a cup of water and sufficient salt.
Cook for three whistles on high flame and switch off. Allow pressure to go by itself.
Open the lid, add the coconut milk and garam masala powder and cook on simmer for 5 minutes. Switch off and adjust seasoning.
Heat oil and splutter the mustard seeds. Add the curry leaves and shallots and fry well till browned. Add into the curry and keep closed for a few minutes.
Serve warm with rice or chapathis.