Put the cubed potatoes and diced tomatoes with salt and turmeric and 1 cup water in a pressure cooker and cook till potatoes are soft but retain their shape.
In a wok, heat the ghee, now add all the rest of the ingredients one by one to make the tadka - add jeera, hing, ginger and green chillies
Pour the mixture of potatoes and tomatoes from the pressure cooker into the wok and bring to a boil letting some of the liquid evalporate on high heat.
The end result should be potatoes in a viscous gravy (not thin)