1.In a medium saucepan, heat buttermilk, sugar and vanilla over low heat until sugar dissolves. Remove from heat.
2.Meanwhile, sprinkle gelatine over water in a small heatproof jug; place jug in a small saucepan of simmering water, stir until gelatine dissolves. Cool slightly.
3.Stir gelatine mixture into buttermilk mixture. Strain through a fine sieve into a jug; cool to room temperature.
4.Scoop pulp from passionfruit. Press pulp in a sieve over a bowl until you have 1/3 cup (80ml) passionfruit juice. Stir juice into buttermilk mixture; pour into six lightly greased dariole moulds (2/3-cup/160ml capacity). Cover; refrigerate for 6 hours or overnight until firm.
5.Slice melons and pineapple; remove pulp from extra passionfruit.
6.To serve, place a warm cloth on moulds, turn out onto serving plates. Serve puddings with fruit.
Must be made at least six hours ahead. Not suitable to freeze. Suitable to microwave.Note