First grease the pan.Now Let the milk to boil in a heavy pan.
Let it reduce to half.

Add lemon juice. Milk will start to curdle. Do not use more lemon juice, otherwise milk will get separated in two portions, solid white and water. It should just curdle little.

Add sugar and ghee and mix continuously.
Cook till milk water is completely evaporated. Gently stir thought out the process.

Cook till all milk reduced and its start leaving the pan.Turn off the heat.
Immediately transfer this to a square greased pan

Cover it with Towel or foil paper. Let it set for 3-4hours.
Remove the cover and cut into square or rectangular pieces.

Garnish with pistachios