Heat oil in a separate pan. Add cumin seeds and when cumin seeds splutter put ginger and tomato paste into the karahi and cook for 5 minutes on low flame. Add salt, red chilli powder, turmeric powder and garam masala and mix well and saute for 2 minutes. Now Add potatoes and mix well and cook for 5 minutes on low flame till oil leaves the karahi. Garnish with coriander leaves.