Rinse a large, heavy-based saucepan with cold water (don’t dry the pan, this helps to stop the milk from catching). Add milk and cardamom, place over very low heat and keep just below simmering point. Cook for 2 hours, stirring occasionally to stop a skin forming and milk catching on the bottom, or until reduced to 375ml (1½ cups). Add palm sugar and stir until sugar dissolves. Strain and transfer to a food processor.
Add pistachios and mango to food processor and process until smooth, then pour into 6 kulfi moulds (see note) and freeze for 6 hours or until firm.
Unmould kulfi by dipping mould briefly in hot water and running a small sharp knife around sides of mould. Invert onto serving plates and serve with mango wedges and slivered pistachios.
Note Aluminium kulfi moulds are available from Indian grocery stores. They’re conical in shape, with flattened tops and screwcap lids. If unavailable, use 1/3 cup-capacity dariole moulds.