Place flour, icing sugar and butter in a food processor and process until mixture resembles fine breadcrumbs. Add egg yolk and water and process until mixture just comes together. Turn onto a lightly floured surface and knead until just smooth. Shape into a disc and cover with plastic wrap. Place in the fridge for 30 mins to rest.
Roll out the pastry on a lightly floured surface to a 3mm-thick rectangle. Line an 11cm x 34cm tart tin, with removable base, with the pastry. Use a small knife to trim the edges. Place in the fridge for 30 mins to rest.
Preheat oven to 200°C. Line the pastry with baking paper and fill with pastry weights or rice. Bake for 10 mins. Remove paper and weights or rice. Bake for 10 mins or until just golden. Set aside to cool completely.
To make the cherry filling, combine cherry, raspberries, blackberries, sugar, vanilla, cinnamon, star anise, orange juice and orange rind in a saucepan. Cook, stirring, for 5 mins or until fruit releases its juices and sugar dissolves. Combine cornflour and 2 tbs cold water in a bowl. Add to cherry mixture. Cook for 2 mins or until mixture boils and thickens slightly. Remove and discard the star anise. Pour into the pastry case. Place in the fridge for 1 hour to chill.
To make meringue, place egg whites and sugar in a heatproof bowl over a saucepan of simmering water. Carefully use an electric mixer to whisk for 6 mins or until heated through. Remove from heat. Continue whisking for 2 mins or until mixture is thick and pale and sugar is dissolved. Place in a piping bag fitted with a 1cm plain nozzle. Pipe meringue evenly over cherry mixture.
Preheat grill on low. Place the tart under grill for 1-2 mins or until the meringue is light golden. (Alternatively, use a kitchen blowtorch to toast.) Cut into slices to serve.