Peel and boil the potatoes in salted boiling water for 4-5 mins till its tender.
Heat the wok and then dry roast the green cardamom. Remove them and then add the rest of the spices. Roast them on medium heat till they are fragrant. Remove the skin of the cardamom and grind it with all the spices, except cinnamon.
Also make a paste of the blanched pistachios or almonds with 1-2 drop of milk.
Prick the potatoes (peeled or unpeeled). Heat ghee in the wok. Add a pinch of turmeric and fry the potatoes, till a nice brown crust forms on the outside and they are fork-tender. Remove the fried potatoes from the pan and place on a tissue.
Add chopped onion in the same oil. And fry till lightly brownish, about 5-6 mins. Now add the ginger-garlic paste, ground spices and red chilli powder. Saute for 2-3 mins, till the mixture dries.
Now remove the wok from heat and slowly add the yogurt, mixing it continuously to avoid cuddling. Keep it back on the flame and add the potatoes. Let the mixture come to a boil and the ghee separate (keep mixing in between).
Add about 1/3rd cup water, mix well and cover the gravy. Keep it on simmer and cook for 12-15 mins, till the gravy thickens and envelopes the potatoes. Add pistachio paste and salt. Cook for another 2-3 mins till the paste blends well.
Serve hot with chopped coriander, rice or roti.