In a wide pan, add a teaspoon of oil/ghee and roast the cashew-nuts and raisins. Once they turn golden brown and raisins plump up, remove it from the pan to a plate. Keep aside until use.
To the same pan, add poha/red aval and roast until they turn crisp. Keep the flame simmer and keep stirring to avoid burning of the aval.
To the roasted aval, add thin coconut milk and let it cook in a simmer flame, until poha turn soft and mushy. Doesn't take too long, maximum 8-10 minutes, it will be done.
While the poha is cooking, take the grated jaggery in a pan, add ¼ cup of water and heat, let it melt completely, strain for impurities and keep it ready for use.
Do not add more water here to melt the jaggery. As this would be added back to kheer, it might thin the kheer and will take a bit of time to boil and reduce.
Once the poha/aval is cooked, add the strained jaggery to the payasam, let it cook for another 8-10 minutes. Add crushed cardamoms now.
After 10 minutes, add the thick coconut milk. Let it sit on the stove for another 5 minutes for the flavors to mingle.
Do not allow it to boil, let it be on simmer flame. Remove it from the stove, add roasted cashew-nuts on top and serve warm.