Make the Spice powder: Dry roast the ingredients under Spice powder until fragrant, about 30seconds. Cool and grind to a powder.
To make the Curry: Heat butter and oil in a pan, add chopped ginger and garlic and fry till aromatic. Add onion, green chilies and saute till the onions turn slightly brown around the edges.
Stir in the whisked yogurt, turmeric, salt and cook for 2 minutes.
Add the boiled potatoes and 1~2tsp of ground spices; cook for 5~6 minutes. Add some water if the curry looks too thick.
Finally add the cream and cook till heated through. Garnish with chopped cilantro and serve with rice or roti.