Wash, peel, and grate 4 medium-sized apples (approximately 500 grams) and set aside.
Heat 3 tablespoons of ghee in a non-stick pan over medium heat.
Add the grated apples to the pan and cook for 10-12 minutes, stirring occasionally, until the apples become soft and the moisture evaporates.
Add 1/2 cup of sugar to the cooked apples 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.
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 apple mixture and mix well.
Cook the halwa for another 2-3 minutes, stirring continuously, until it reaches the desired consistency.
Remove from heat and let it cool slightly. Serve warm or at room temperature.