Boil syrup ingredients for 2-3 minutes and strain through a fine sieve to cool.
Boil sugar and water for meringue until the syrup reaches 110°C.
Whisk egg whites in a bowl until firm peaks form.
At 121°C, pour syrup into whites in a steady stream while whisking for 5 minutes.
Blend passion fruit pulp with 50ml syrup and strain through a sieve.
Boil the passion fruit purée with powdered milk and vanilla pod.
Whisk egg yolks and sugar to ribbon stage, add fruit mixture, and thicken over low heat.
Stir drained gelatine into the custard, strain, and set aside to cool.
Fold in half the meringue, liqueur, and whipped cream when the custard is lukewarm.
Brush sponge with 50ml syrup and fruit purée, then cut to fit a 25cm flan ring.
Fill the ring with custard, smooth the top, and freeze for several hours.
Heat syrup and pulp, add gelatine, cool, and spread over the frozen delice to chill.
Release the ring by heating the outside with a blowtorch and sliding it off.
Garnish slices with blackberries, redcurrants, and fresh passion fruit pulp.