In a heavy bottomed pot, heat 3-cups milk and cardamoms over medium heat until it comes to a low boil, stirring often to prevent the milk from burning. Once the milk has come to a boil, reduce heat to medium low and cook for 20 minutes.

Drain rice and transfer to the jar of a blender or food processor. Blitz the rice until it has ground down to a fine sandy consistency. Transfer the ground rice to a small bowl, add the remaining 1-cup of milk, and whisk until smooth.

Add sugar to boiling milk, and stir to incorporate. Once the sugar has melted, drizzle in milk and rice mixture, making sure to stir as you add as to avoid lumps. Cook until the mixture has reduced and thickened, about 30 minutes.

Transfer the Firni to serving dishes, garnish with nuts, and allow it to cool.