In another large mixing bowl add the butter, sugar and salt and then sift in the flour.
Using your fingertips, crumble all of the ingredients in the bowl together until you are left with a bread crumb consistency. Or you can use your food mixer and the paddle attachment to do this for you.
Add the cold water to the crumble mix and using your hands, mix all the ingredients together letting the water absorb into the crumble mix allowing it to form a soft pastry ball. If the pastry is still too dry and crumbly, just add a little more water a few drops at a time until the pastry is tacky but doesn’t stick to your hands.
Split the pastry in half and set one half to one side for the time being.
Take the other half of the pastry and use a rolling pin and a dusting of flour to roll the pastry out flat, I rolled mine out to measure approximately 3 mm thick. The pastry will also need to be rolled out wide enough to cover the base and the sides of your pie dish.
Trim off any pastry hanging over the sides of the pie dish with a sharp knife to neaten.
After half an hour has passed, the apples that have been macerating will be ready to add to the pie dish.
Give the apples a good stir, drain them gently and then pour them into the pie dish, over the pastry.
Take the other half of the pastry and roll it out flat. The pastry should be rolled out big enough to cover the top of the pie dish, thus forming the pie lid. Before placing it on to the top of the pie cut out several little star shapes.
Beat one egg in a bowl and brush the beaten egg over the top of the pie.
Sprinkle a tiny amount of the brown sugar over the top of the pie. Rub it in gently. This gives the pie a lovely golden top.
Bake in the oven for approx 30 mins. I say "approximately" as my oven is very fierce but yours may be gentler. You want the apples to be softened and the pastry to be golden brown so just keep an eye on it.
If you cut in to the pie straight out of the oven you may find quite a bit of juice at the bottom. Allowing the pie to rest for 30 mins or so will allow the pastry to soak all of these juices up so don't worry.