To prepare the squash, add 2 cups water into the steel inner pot, then place a steamer basket into the pot. Place the peeled and cut squash in the basket.
Secure the lid, close the pressure valve, press the steam button and set the time to 15 minutes at high pressure.
Open the valve to quick release any remaining pressure.
Remove the squash and steamer basket from the pot. Set the squash aside for now.
Dump out any water still remaining in the bottom of the pot.
Press the sauté button and add the ghee and the squash. Mash the soft squash with a spoon, then add sugar and cardamom. Stir-fry for 3-4 minutes, or until the halwa turns a shade darker and the ghee releases a nutty aroma.
Garnish with crushed nuts and serve.