Rinse the aval quickly with water. Don’t let it soak or stay in water for more than just a few seconds or it will disintegrate into the water.
Heat the 4 tbsp ghee in a heavy bottomed pan and add the drained aval to it. Roast for a few minutes over medium heat till all the ghee is absorbed and the aval starts to slightly crisp up. Now add the milk to this and let it come to a boil. Lower the heat and let it cook for 10-15 mins. Add sugar and let all the sugar melt. Cook for a several more minutes till the milk reduces a little and starts to turn a little pink. Add ground cardamom and mix well.
Heat the 1 tbsp ghee in a sauté pan and add the cashews to it. Once the cashews brown, pour it all on to the payasam. Serve immediately or once it has cooled down a bit.