Heat oil in a pan.
Pplutter mustard seeds, add onion, ginger and green chillies and saute(by adding salt) till onion becomes transparent.
Add turmeric powder and diced potatoes, saute for 2 minutes.
Add IInd extract of coconut milk.
Cover it with a lid and cook till potatoes are done and the dish reaches a thick consistency.
Add Ist extract of coconut milk and pepper powder.
Mix it well and remove from fire.
Don`t allow the dish to boil after adding Ist extract of coconut milk.
Sprinkle garam masala over the dish and serve hot with chappathi, appam,ididappam or parotta.