Pour the milk into a large, heavy-based saucepan. Bring it to the boil, then reduce the heat to low and simmer for 3 hours, stirring every 5–7 minutes to ensure the milk does not stick to the bottom of the pan.
Once the milk has reduced by two-thirds, measure it to ensure the volume has reduced to 500ml, then return it to the pan. Add the sugar and cardamom and stir for 1 minute, then add the pistachios. Pour the mixture into a jug and leave it to cool a little.
Divide the mixture between 6 kulfi cones (use plastic containers if you don’t have any) and freeze overnight.
When ready to serve, dip the cones in warm water for a few seconds, then turn out the kulfi onto individual serving plates. Sprinkle with the extra pistachios to serve.