Grease a square or rectangular tray (about 8x8 inches) with ghee and line with parchment paper. Set aside.

In a heavy-bottomed non-stick pan, heat ghee over medium-low heat. Add the grated khoya and cook, stirring continuously, for 5-7 minutes until it softens and starts to come together.

Add sugar to the pan and continue to cook, stirring. The sugar will melt and the mixture will become slightly liquid. Keep cooking until the mixture thickens and leaves the sides of the pan, about 8-10 minutes.

Stir in the cocoa powder and cardamom powder (if using). Mix well until the cocoa is fully incorporated and the mixture is uniformly chocolate-colored. If the mixture looks too dry, add a tablespoon of milk.

Continue cooking for another 3-5 minutes on low heat, stirring constantly, until the mixture becomes very thick and forms a lump that doesn't stick to the pan.

Immediately transfer the hot barfi mixture to the greased and lined tray. Spread it evenly using a spatula or the back of a spoon.

Let it cool completely at room temperature for at least 2-3 hours, or refrigerate for 30 minutes to speed up setting.

Once set, gently lift the parchment paper and transfer the barfi to a cutting board. Cut into desired shapes (squares, diamonds).

Garnish with silver leaf or chopped nuts, if desired, before serving.