Add the ricotta cheese, sugar, and water to the pot and mix well.
Secure the lid, close the pressure valve, and cook for 11 minutes at high pressure. (This is a good time to grind cardamom if you don’t have some on hand).
Add ghee, milk powder, and cardamom to the pot and stir until well combined (you may want to wear a glove to hold onto the hot pot as you stir).
Pour the mixture into a parchment-lined 8×8 pan, sprinkle chopped pistachios over top, and then gently shake the pan to help level the fudge and also to help the pistachios stick.
Let the milk cake cool down (takes about an hour), then put it in the fridge for 3 hours to set.
Once chilled, lift from the pan using parchment then cut into 1.5-inch x 1.5-inch squares.
You can store this mithai in an air-tight container in the fridge for about a week.