Pour the milk in a heavy bottomed non-stick pan and bring it to a boil.
Add Lemon juice/ citric acid and mix well. At this point, the milk is slightly curdled but the whey does not separate.
Boil till the milk turns thicker and reduces to half, stirring continuously.
Add condensed milk and stir continuously.
Continue boiling and stirring till it thickens and resembles Khoya. Keep stirring for about 45 minutes on a low to medium flame till all the liquid evaporates and turns dry.
Add the ghee and stir for 10 minutes.
Keep cooking till its light brown.
Grease a 6″ by 6″ cake tin with ghee and transfer the hot milk cake mixture in it. Garnish with chopped nuts and cover with aluminium foil immediately.
Let it cool to room temperature and cut into squares.