Melt the ghee in a heavy-bottomed pan over medium heat. Add the grated sweet potatoes and sauté for about 10 minutes, stirring occasionally, until they soften and begin to release their moisture.

Next, pour in the milk and bring the mixture to a simmer. Stir in the sugar and continue to cook, stirring frequently, for another 10 minutes until the sweet potatoes absorb the milk and the mixture thickens.

Add the crumbled khoya and cardamom powder, mixing well to incorporate. Cook for an additional 5 minutes, allowing the halwa to reach a desired consistency.

Finally, stir in the chopped nuts and raisins, if using. Cook for another 5 minutes before removing the halwa from the heat.

Serve warm, garnished with additional nuts if desired.