Grate the carrots with the fine blade of your food processor or with a box grater.
Melt the ghee in a stovetop pressure cooker over medium heat. Meanwhile, crush the cardamom pods in a mortar and pestle or with a heavy saucepan. Discard the papery pods and crush the seeds to a semi-fine powder. Add to the ghee and saute until fragrant, about 30 seconds.
Tumble the grated carrots into the scented ghee. Cook, stirring every now and then, until slightly deepened in color, about 3 minutes.
Pour in the milk, sugar and a good pinch of salt. Stir and bring to a boil. Twist the lid in place and ensure it is sealed (refer to the manufacturer's guide for locking the lid). Pressure cook on high for 3 minutes. Follow the guide again for quick-release of pressure, then carefully open and stand back!
Place over high heat again. Stir in the powdered milk and currants and cook, stirring often, until most of the liquid has evaporated, about 10 minutes. The halwa should have a puddinglike consistency. Sprinkle with the pistachios and serve either warm or cold.