Begin by making the pastry.
In a large bowl, rub the chilled, cubed butter into the flour with your fingertips.
Mix until it resembles fine breadcrumbs.
Add the egg yolk and a little cold water to bind the mixture.
Wrap the dough in cling film and chill for 30 minutes.
Preheat your oven to 375°F.
This gives you time to prepare the apple filling.
Combine the sliced apples with caster sugar, cinnamon, and lemon juice.
This helps prevent browning and adds a lovely flavor.
Roll out the chilled pastry and line a 9-inch pie dish with half of it.
Place half of the apple mixture into the dish.
Distribute the apples evenly for consistent baking.
Cover the apples with the remaining pastry.
Seal the edges with a fork or your fingers.
Make a few slits on top for steam to escape.
Brush with the beaten egg for a beautiful golden crust.
Bake in the preheated oven for about 45 minutes, until the crust is golden brown.
The apples should be tender and the filling bubbling.
Once done, let it cool slightly before serving.