In a large skillet, fry potatoes in ghee until brown. Remove and reserve the potatoes. Add onion, garlic and ginger to the skillet, fry until onion is soft and golden. Add chili, pepper, turmeric, cumin, salt and the tomatoes. Fry, stirring constantly for 5 minutes. Add yogurt, mint, cardamom and cinnamon stick. Cover and cook over low heat, stirring occasionally until the tomatoes are cooked to a pulp. It may be necessary to add a little hot water if the mixture becomes too dry and starts to stick to the pan.