Thaw the spinach and blend using a blender until a paste is formed. You may need to add water (in tiny quantities to help the blending process). Add the panir and blend further. Chop the onion and potatoes any way you like. In a saucepan toast the cumin seeds. When the seeds start to crackle add the onions and water. Sauté until the onions turn light brown. Add the potatoes and cover the dish. Cook for about 2-3 minutes making sure that the potatoes don't burn. Add the chili powder and turmeric, stir. When the potatoes are semi-hard, add the spinach-panir blend. Stir and let it simmer for about 5 minutes, add salt and let it simmer for another 10 minutes.