Mix the flour, salt and sugar in a bowl. Add the butter and rub together using your hands to form an even, crumbly mixture. Pour in the water and mix quickly to form a soft dough; do not knead. Cover and chill for approx. 30 mins.
Line a round tin (approx. 30 cm in diameter) with baking paper. Roll out the pastry on a lightly floured surface, transfer the pastry to the tin and prick firmly.
Blind bake for approx. 10 mins. in the lower third of an oven preheated to 200°C. Remove from the oven, leave to cool.
Cut open the vanilla pod lengthwise, scrape out the seeds, mix in a bowl with the egg yolks and sugar.
Combine the milk and cornflour, bring to the boil while stirring, gradually pour into the egg yolk mixture, stirring constantly. Pour the mixture back into the pan, bring to the boil while stirring constantly, simmer and continue to stir for a further 15 secs. Remove from the heat, stir for a further 2 mins. Pour the custard through a sieve into a bowl, leave to cool.
Spread the vanilla custard on top of the pastry base, top with the apples and hazelnuts.
Bake for approx. 20 mins. in the lower third of an oven preheated to 200°C.
To make the meringue, beat the egg whites with the sugar until stiff, mix in the cinnamon and beat briefly. Remove the tart from the oven. Spread the meringue on top of the apples, bake for a further 5 mins.