Heat the ghee in a heavy-bottomed pan and roast the cashew nuts until golden
Drain and set aside
Add raisins to the same pan and fry until they puff up
Drain and set aside
To the same pan with ghee, add the sago and lightly roast until they turn a very light brown
Top up with 1 cup water + 1/2 cup milk
Cook on low flame until the sago turns soft and gloopy
Add the remaining milk and bring to boil
Continue to simmer and cook until the milk reduces to about 2/3 volume, about 15-20 minutes
The payasam will turn thicker due to the starch from the sago
When the milk has thickened to the desired consistency, add the condensed milk (if using) and sugar
Mix well and bring to a gentle simmer
Finally add the cardamom powder and roasted cashew nuts + raisins
Give everything a final stir and remove from heat
Serve warm or chilled
As the payasam cools down, it will become thicker so add more milk before serving for looser consistency