Start with making your pastry: In a large bowl, cream the butter and sugar together until light and fluffy. Add the egg and mix through.
Sift in the flour and combine until the pastry comes together, using your hands to bring together if needs be.
Wrap the pastry in cling film and refrigerate until required.
Pre-heat your oven to 180°c (160°c for fan assisted oven or Gas Mark 4) and grease a 20-22cm loose-bottom pie tin before dusting with a little flour. Set aside.
Roughly chop your apples and set aside. In a small bowl, mix the sugar, cinnamon & cornflour and set aside.
Take your chilled pastry from the fridge and remove about 1/3 of it, setting it aside for the top of the pie Roll the remaining pastry on a well floured work surface until it is big enough to line your pie tin.
Gently lift the pastry into your pre-greased/floured pie tin, pressing it into the edges and uses any excess pastry to patch up any breaks or holes.
Add your apples to your pastry lined pie tin, ensuring they are evenly distributed and sprinkle the sugar mixture on top.
Roll your remaining pastry until it is large enough to cover your pie. Wet the edges of your pie with a little water, before transferring the pastry lid to the top, pressing the edges together to seal the pie. Again, patch up any holes or breaks with excess pastry.
Trim the edges of pastry, before making a few holes on the top to allow the steam to escape whilst baking.
Bake in your pre-heated oven for around 40-50 minutes, until golden on top.
Remove from the oven and sprinkle with some caster sugar whilst still hot.