Wash basmati rice and drain.
Heat ghee in a pressure cooker, toast cashews until golden, then set aside.
In same ghee, crackle mustard seeds, curry leaves, ginger paste, and sliced onions; sauté until translucent.
Add finely chopped tomatoes, turmeric powder, and salt; cook until tomatoes turn soft.
Stir in rice and water, cover cooker, and cook for 2 whistles on medium flame.