Place the milk and tea bag (if using) in a saucepan and gently simmer for 3 minutes. Take the pan off the heat and discard the bag.
Bash open the cardamom pods and smash the seeds with a pestle and mortar till crushed. Add to the milk. Rinse the tapioca under cold running water and add to the milk. Stir in the coconut milk and golden caster sugar.
Return the pan to the heat and simmer gently for 30-40 mins, stirring regularly, until the mix is thick and creamy. Serve the tapioca sprinkled with sugar, berries and crushed pistachios.