In a medium saucepan, combine the granulated sugar and water. Bring to a boil over medium heat, stirring until the sugar is completely dissolved.
Reduce the heat to low and let the syrup simmer for about 10 minutes, until slightly thickened.
In a small bowl, whisk together the cornstarch and a little cold water until smooth and no lumps remain.
Gradually add the cornstarch mixture to the simmering sugar syrup, stirring constantly to prevent lumps from forming.
Continue to cook over low heat, stirring constantly, until the mixture thickens and becomes translucent.
Stir in the ghee (or unsalted butter), ground cardamom, soaked saffron along with its water, and rose water. Mix well to combine.
Add the chopped almonds and pistachios, and continue to cook for another 5-10 minutes, stirring constantly, until the halwa pulls away from the sides of the pan and has a glossy appearance.
Transfer the halwa to a greased serving dish or individual serving cups. Smooth the top with a spatula.
Garnish with additional chopped nuts and edible silver or gold leaf, if desired.
Allow the halwa to cool to room temperature before serving.
Enjoy your meal!