Rinse the basmati rice in cold water until the water runs clear. Cover with water and let soak for 20 minutes, then drain.

Pour the full-fat milk into a heavy-bottomed pot and bring it to a boil over medium heat, stirring occasionally to prevent a skin from forming.

Reduce the heat to low. Add the drained rice to the simmering milk and stir well.

Simmer uncovered for 35 to 45 minutes, stirring frequently and scraping down the sides of the pot, until the milk has reduced by half and the rice grains are completely soft and mushy.

Stir in the sugar and green cardamom powder. Cook for another 5 minutes until the sugar is fully dissolved and the kheer reaches a thick, creamy consistency.

If desired, heat the ghee in a small pan and lightly fry the mixed nuts until fragrant, then stir them into the kheer. Serve warm or chilled.