Boil potatoes, peel and cut into small pieces. Heat oil and add tumeric, green chillies, garlic, and ginger. Fry for 1 minute. Add yogurt, potatoes and salt. Cover and cook gently for 4-5 minutes. Garnish with green coriander leaves. Note : If desired water can also be added after frying potatoes and boil it for 5 minutes to give it the right consistency.