Heat 2 tablespoons of oil in a shallow frying pan. Add cumin, mustard seeds, and red chillis. Fry for a few seconds till seeds splutter. Add curry leaves, asafoetida, and turmeric. Fry for 30 seconds.
2. Add the potatoes, and fry for 5 minutes till they brown on the outside. Add salt to taste. Sprinkle some water on the potatoes, cover with lid, and cook for 10 minutes, or until the potatoes are cooked, but still firm. Make sure the heat is not too high or they will stick to the bottom of the pan.
Meanwhile, heat remaining 1 tablespoon of oil in another frying pan. Add spinach, and cook on high heat till it wilts. Add salt and cook a few minutes more so all the excess water evaporates.
4. Add spinach to the potatoes. Mix well. Add red chilli and cumin powder. Check the salt and add more if needed. Cook for 5 - 10 more minutes for spices to mix well. Serve hot.