Preheat the oven to 170 °C. Grease the cake tin with butter.
Combine the butter, caster sugar and egg yolk to make the tart base. Add the flour, a pinch of salt and the vanilla sugar. Knead to create a smooth dough. Wrap the dough in plastic film and leave to rest in the fridge for 15 minutes.
Lightly dust the work surface with flour. Roll out the dough with the rolling pin until you have a piece of dough of 5 mm thick that fits the cake tin. Line the cake tin with the dough. Prick the base with a fork. Place the cake tin in the oven and bake for approx. 13 minutes until golden and cooked.
To make the creme patissiere, whisk the egg yolks with 75 ml of milk and the flour in a bowl until smooth. Place the rest of the milk ,the caster sugar and the vanilla sugar in a saucepan and bring to the boil. Pour the hot milk into the saucepan with the egg yolks. Stir then transfer back to the other saucepan. Gently bring to the boil. Keep stirring until the mixture forms a thick custard cream. Spoon the cream onto a plate. Cover with plastic film that touches the surface of the cream. Leave to cool.
Halve the maracujas and scoop out the flesh with a spoon. Add to the cream custard mixture. Put in the fridge until needed.
Remove the tart base from the tin. Coat the base with the maracuja creamed and put the tart back into the fridge.
To make the meringue, beat the egg whites in a spotlessly clean bowl with the mixer until white and frothy. Add the caster sugar spoonful by spoonful. After each spoonful, beat the egg whites until the crystals have dissolved and the mixture forms soft peaks. Mix the cornflour with two teaspoons of water and fold gently through the meringue mixture. Spread the meringue over the tart base. Create peaks with a fork. Use the crème brûlée torch to brown the meringue.
Tip: If you prefer to leave out the raw eggs, use pasteurised egg white to make the meringue.
