Start off by cutting the peeled potatoes into coins, about 1/5 inch thick. Then soak them in water for atleast 10 minutes before cooking.
While the potatoes are soaking in the water, heat the oil in a large pan. Add the onions and saute till they start turning golden brown. Then add the ginger, garlic and chopped tomatoes. Saute for two minutes, then cook covered for 5 minutes on a low flame.
Break the tomatoes and onions down with your cooking spoon, then add all the spices barring the kalongi. Saute for one minute, then drain the potatoes and add them to the masala. Mix well so the potatoes are all covered by the masala and cook for 5 minutes covered. At this point add the kalongi , mix well, then cook covered on a low flame for another 10 minutes or so, until the potatoes are cooked thorugh. Mix occasionally so the poattoes don't stick to the bottom.
Taste for salt and spices, adjust accordingly and serve with a garnish of fresh coriander. These go great with some steamed basmati, with naan or roti.