Cut the potatoes into one-inch pieces and soak them in water in a large bowl. Soak poppy seeds in one cup warm water in another bowl for 15-20 minutes.
Drain and grind poppy seeds to a fine paste.
Heat mustard oil in a non-stick pan till it begins to smoke. Take the pan off heat and let the oil cool. Heat it again on medium heat and add onion seeds and saute till fragrant.
Add potatoes and saute on medium heat for around 5 minutes.
Add poppy seeds paste and mix. Add ½ cup water and cook on low heat till the potatoes are almost cooked.
Add salt and slit green chillies, mix and cook for 3-4 minutes or till the potatoes are completely done.
Transfer into a serving bowl, drizzle pure ghee on top and serve hot.