Peel and deseed 1 kg of ripe papaya. Grate the papaya and set aside.
In a heavy-bottomed pan, heat 2 tablespoons of ghee on medium flame. Add the grated papaya and cook for 10-12 minutes, stirring occasionally, until the moisture evaporates and the papaya becomes soft.
Add 200 grams of sugar to the cooked papaya and mix well. Cook for another 5-7 minutes, stirring continuously, until the sugar dissolves and the mixture thickens.
Add 1/2 teaspoon of cardamom powder and mix well. Cook for another 2-3 minutes.
In a separate pan, heat 1 tablespoon of ghee and roast 1/4 cup of chopped mixed nuts (cashews, almonds, and pistachios) until golden brown. Add the roasted nuts to the papaya mixture and mix well.
Cook the papaya halwa for another 2-3 minutes, stirring continuously, until it reaches the desired consistency. Turn off the heat and let it cool slightly before serving.