1. Pre-heat the oven to 180°c/gas 4.
2. For the pastry: whizz the flour, icing sugar and a pinch of sea salt together for a few seconds in a food processor, then add the butter. Whizz for another few seconds, until it looks like coarse breadcrumbs.
3. Whisk the egg yolk and 3 tbsp of ice cold water together and pour it into the flour mixture. Whizz until it collects into a ball. Wrap in clingfilm and chill for 1 hour.
4. Later, take out the pastry, allow to warm slightly and roll it out to a few millimeters thickness. Upturn the pie dish onto the centre of the pastry and use it as a template – adding an extra inch all the way round – and cut out the top crust. From the remnants of the pastry, cut out a 5cm thick strip. Arrange this strip of pastry so it covers the whole rim of the dish and press into place. Put the 2 pie raisers in the middle of the dish.
5. Quarter, core and peel the apples, then cut into chunky slices. Layer the slices with generous sprinkles of sugar between, until they form a big heap around the pie raisers. Brush the pastry rim with cold water, then cover with the top crust. Pinch the pastry rim and crust together, crimping to make a tight seal.
6. Make a few slashes in the top crust, then put the pie in the fridge to rest for at least 30 minutes.
7. Before baking, brush the top crust with the egg white, and then sprinkle with castor sugar. Bake for about 45 minutes, or until the crust is golden brown. Serve warm.