Place jaggery and water in a deep pan over low heat. When jaggery melts, remove from heat, and let it cool. Pass it through a sieve to remove all the impurities, if needed.(For full instructions with pictures about how to melt jaggery, click here). Set aside.
To Fry Cashews and Raisins:
Heat ghee and oil in a frypan over medium-high heat. Add raisins, and fry until it becomes plump. Remove from pan. Drain on an absorbent towel. Add cashew nuts to the same pan. Saute until golden. Remove from pan. Drain on an absorbent towel.
To Make Payasam/ Pudding:
Heat pan, and roast instant oats over low flame. Stir continuously to prevent it from burning.
When it turns light brown, add jaggery syrup and water. Mix well. Bring to a boil. Simmer for 2-3 minutes. Add thin coconut milk. Simmer for another 2-3 minutes.
Stir in thick coconut milk. Simmer again for another minute. Add water if payasam is too thick. Stir in a teaspoon of ghee and remove from heat.
Garnish with fried cahews and raisins. Serve oats payasam hot or cold.
Notes
As oats cook really fast, do not leave it unattended To make this dessert gluten free, use gluten free oats