Heat the oil in a large pan or wok and keep the heat on medium / high.
Add the cumin seeds when hot and fry for a couple of minutes until they start browning and smelling lovely.
Throw in the chopped onions and try until they start browning.
Add in the chopped ginger and garlic and fry off for a couple of minutes or until they're just starting to brown.
Add the chopped tomatoes, green chillies if using, salt, chilli powder if using and turmeric. Mix and let everything heat until it starts bubbling. Then turn the heat to medium and leave for 10 minutes.
Now the oil should start separating, i.e. you should see oil rising to the top. If not wait a little longer and stir if its starting to stick.
Now throw in the cubed potatoes and fry until coated.
Add ½ cup of water and cook for around 15 minutes or until the potatoes are softened.
Now add the spinach, fenugreek powder if using, garam masala and mix everything together well.
Over and cook for 15 minutes.
Mix in the ghee or butter and wait a few minutes for everything to combine.
Enjoy