Process pistachios in a food processor until fine; add milk, cornflour and condensed milk and blend for 1/2 minute.
Transfer mixture into a saucepan and heat over low heat, stirring all the time, until thickened. Pour into individual ramekins or a 1.5L mould; cool to room temperature. Cover with cling film, then transfer into fridge to chill for 3 hours.
Place passionfruit pulp and sugar in a small saucepan; simmer over low heat until sugar dissolves and sauce thickens. Cool sauce before serving with pistachio custard pots.