Heat butter and oil in pan and add onions, garlic, ginger and chillis, stir fry on medium heat for two mins, stirring frequently. Add potatoes and stir fry for 5 mins, then add tumeric, salt , coriander, cumin. Cook for 15 mins or until potatoes are tender, I put the lid on at this stage and checked it every 5 mins or so and stirred. Sometime during this process I added a little water to stop sticking. When potatoes were cooked I added 2 bags of spinach which I had chopped and then replaced the lid to allow spinach to wilt slightly. When spinach has wilted stir into the potatoes and spices. Serve as a side dish with curry!