Dissolve the custard powder and sugar/honey in 1/2 cup of cold milk in a large bowl and keep it aside. Similarly, mix the thandai powder in 3-4 tbsp of milk and keep it aside. Heat the rest of the milk to nearly boiling point on medium heat.
Add the hot milk to the custard mix and stir well. Pour the mixture in the saucepan and bring it to a boil on gentle heat, stirring continuously.
Finally add the thandai powder paste to the custard and continue boiling on gentle heat, stirring continuously for 2-3 minutes until very thick (The custard is going to be quite thick as it needs to set in the tart.)
Take it off the heat and strain the custard to remove all the bits of spices or lumps, stir gently with the spatula to move things around. Let it chill.
For the tart shell, mix melted butter with crushed biscuits. Press this mixture onto the tart tin tightly and chill it in the fridge for an hour or so until set.
Pour the thick custard in the chilled tart ba-se and spread it around with a spatula.
