1 For the pastry: sift the flour into a mixing bowl and stir in the sugar and salt. Rub in the butter until the mixture resembles breadcrumbs. Add the egg yolk, mixing continuously until the mixture just comes together as a dough. If it is too stiff, add a little water. Roll the dough into a ball, then wrap in cling film and chill for 30 minutes.
2 Heat the oven to 180°C (160° fan) 350°F gas 4. Grease a 23 cm|9" deep flan tin.
3 Roll out the dough on a floured surface and line the tin. Prick the pastry all over with a fork, line the pastry case with non-stick baking paper and fill it with rice or dried beans. Bake for 10 minutes. Remove the paper and beans.
4 For the filling: make the custard according to the directions on the packet, using the wine and apple juice instead of milk and the sugar.
5 Chop 2/3 of the apples and thinly slice the rest. Mix the chopped apples with the apple custard.
6 Whisk the egg white until stiff and fold into the apple custard. Spoon into the pastry case.
7 Arrange the sliced apples on top of the filling and bake for 40 minutes until the apples are beginning to brown and the filling is set. Brush the apples with the apple jelly while the tart is still warm. Leave to cool.