Take 1 litre milk in a wide and heavy bottom pan. Put it to boil.
Once it comes to a boil, switch off the flame and remove the pan from the stove put. Add in the lemon juice till the milk starts to curdle.
Using a strainer, drain the liquid and keep the paneer/chena aside.
In another heavy bottom pan, put the remaining 1 litre of milk to boil.
Continue boiling till the milk starts to thicken, keep stirring the milk at regular intervals else it might get stuck at the bottom. After around 20 minutes add the chena that we prepared before to the milk. Continue stirring the mixture continuously. Keep the flame at medium-low heat.
Cook the mixture for another 10 minutes or so and add the cardamom powder.
The mixture will start to get really thick now. Add powdered sugar, ghee/butter and mix. Once you add the sugar, the mixture will again become little thin. Keep cooking till it starts becoming thick again.
Once the mixture reaches a consistency where it's looks like it will set, switch off the flame and keep the pan aside. Take a tray/plate, grease it with little butter or ghee and pour the mixture on it. Press the mixture using a spatula or your hands,
Garnish with pistachios, slightly press the nuts into the mixture. Let the mixture cool down for 2-3 hours before cutting into pieces