1. Preheat the oven to 180C fan (200 C/gas 6). Lay non-stick silicone liners on two baking sheets.
2. Whisk the egg whites in a large, clean bowl until the form stiff peaks, then whisk the caster sugar, a little at a time. Fold in the lemon verbena. Divide the meringue mixture equally between the baking sheets and gently spread each portion into a 17.5cm (7in) round.
3. Bake the meringue rounds on the centre shelf of the oven for 5 minutes. Turn the oven off and leave the meringues inside to dry out for at least 4 hours.
4. For the filling, put the mango dice in a mixing bowl. Cut the passion fruits in half and scrape out the pulp and seeds into the bowl. Add the orange zest and juice and sugar. Mix together and set aside.
5. Whip the cream to soft peaks, then fold in the marscapone and sticky seeds scraped from the vanilla pod. Carefully spread half the mixture over one of the meringue rounds, then spoon the mango and passion fruit over the cream. Place the other meringue on top. Spread the remaining cream mixture over it and decorate with the toasted pistachios. Dust with icing sugar to serve.