Boil milk (without adding any water) and keep aside.
In a heavy bottomed vessel, sprinkle two tablespoon sugar and keep it on medium flame. Do not stir. After few seconds, it will start melting and then it turn brown (caramelized). Now add just two tablespoon water and mix well.
Add the boiled milk and stir well. Bring it boil once again. Add rawa or rice flour mixed with little water. Reduce the heat and stir well. Add remaining sugar and let it boil in low heat. Fry the cashew nuts in ghee and add to the payasam.