Sauté whole spices with cumin seeds and onions in hot oil till lightly browned. Add in tomatoes, ginger-garlic paste, and spices, and cook for a couple of minutes till tomatoes soften and pulp.
Add in lamb, water and salt, and cook covered for about 40 minutes. Add in potatoes, and cook covered for another 20 minutes till lamb is tender and potatoes are cooked through.