Add khoya to a non-stick pan and cook it on medium heat until it turns slightly brown (4-5 minutes), stirring continuously.
Heat ghee in a heavy bottom large size pan over medium heat.
Once the ghee is hot, add almonds and cashew nuts to the pan. Fry them until they are golden brown in color (1-2 minutes), stirring frequently.
Add lauki to the pan and fry for 5-6 minutes, stirring frequently.
Now add whole milk to the pan and mix well. Reduce the heat to low.
Cook the halwa until all the milk has reduced (20-25 minutes). Keep stirring frequently to avoid milk from burning at the bottom of the pan. Add cardamom powder and rose water and cook for a minute.
Add the browned khoya and sugar to the pan and mix everything well. The halwa will become slightly runny at this stage because of the melted sugar.
Cook on medium heat until the halwa has thickened and ghee starts to leave the sides of the pan (15-20 minutes).