Pour the milk into a heavy-based pan and heat gently (you can preheat the milk in a jug in the microwave then transfer the hot milk to the pan, to save time, if you prefer).
Add the cardamom pods and rice to the milk.
Slowly bring to the boil then lower the heat and simmer rapidly, stirring from time to time to prevent the rice from sticking to the bottom of the pan. Simmer, stirring occasionally, until the milk is reduced by about half; this may take as long as 1¼ hours.
While the milk is simmering, roughly chop the pistachios.
When the milk has reduced by half or more, remove and discard the cardamom pods.
Transfer the rice pudding to a bowl. Add the sugar and taste, adding more sugar if you want it sweeter.
Add the chopped pistachios, stir well, and leave to cool.
Cover the bowl with cling film and cool in the fridge for at least four hours or overnight.
When ready to serve, spoon into individual serving bowls. Decorate with vark, if using.