For the pastry, pulse the flour, sugar, butter, ground almonds, baking powder and citrus zests in a food processor until the mixture resembles breadcrumbs.
Add the beaten egg and pulse until the mixture comes together as a dough (adding a little cold water if necessary). Press the dough into a ball, wrap in clingfilm and chill in the fridge for at least 30 minutes.
Preheat the oven to 200C/400F/Gas 6. Grease two six-hole petit four tins.
For the pastry cream, bring the vanilla seeds and milk to the boil, in a saucepan, whisking all the time. Remove the pan from the heat.
Beat the sugar and egg yolks in the bowl for 3-5 minutes, or until the mixture falls in thick ribbons from the whisk. Slowly whisk in the cornflour paste until well combined.
Add the hot milk in a steady stream and when it’s completely incorporated, pour the mixture back into the saucepan. Heat the mixture, whisking contantly, until boiling. Cook for a further minute, then pour the mixture into a bowl. Set aside to cool for 10 minutes, then stir in the elderflower cordial. Cover with the clingfilm and chill in the fridge.
Roll the pastry out on a floured work surface and use it to line the petit four tins. Bake in the oven for 7-10 minutes or until the pastry is golden-brown and crisp. Let the tart cases cool a little then carefully transfer them to a wire rack.
For the glaze, heat the sugar and half the apple juice in a saucepan until boil then remove the pan from the heat.
Dissolve the cornflour in the remaining juice, quickly pour the mixture into the saucepan and return to pan to the heat. Cook until the mixture has thickened, stirring all the time, then add the golden syrup, bring back to the boil and remove the pan from the heat. Set aside to cool
To assemble the tarts, spoon a little pastry cream into each pastry case. Arrange the fruit on top and drizzle over the glaze. Chill in the fridge until ready to serve.