Take milk in a bowl with a heavy base and allow it to boil. When the milk starts boiling, take it off the flame and allow it cool.
Mix some water in lemon juice and when the milk cools a bit, pour in the lemon juice little by little and keep stirring. When the milk coagulates, the milk and chena will separate, once this occurs stop adding the lemon juice into it.
Strain the chena with a cloth and pour cold water over it so that there is no flavor of lemon in the chena.
Take it out in a plate and mash the chena for 5 to 6 minutes until its smooth. Mix in the cocoa powder and cadbury.
Take a non stick pan and place it on the flame. Now place the chena into it, stir constantly and roast it on a low flame for 3 to 4 minutes.
Turn off the flame and take out the chena in a plate. Allow the chena to cool, then mix the cardamom powder into it.
Take a small lump from the mixture, roll and then flatten it gently. Place it over a plate.
Garnish with chopped pistachios and choco chips and relish eating these choco sandesh.