Preheat the oven to 160C.
Grease an oven-safe dish or a large plate.
In a large bowl, Sieve the flour. Add the caster sugar and the diced butter. Using the tips of your fingers, rub the butter into the flour until the mixture resembles fine breadcrumbs. Add in the egg and pour in enough water, little by little, until the mixture comes together into a pliable dough. Set in cling film for 5-10 minutes in the fridge.
In the meantime, in a bowl, combine the apple pieces with the brown sugar, cinnamon. Toss to coat the apple.
Next, remove the pastry from the refrigerator. Divide the pastry into 2 pieces and roll the first part out to line the base of the plate.
Add the chopped apple.
Roll the rest of the pastry , creating a larger circle than the base of the plate. Carefully transfer over the apple mixture.
Seal the edges and clear excess of pastry hanging around the edges. Make an incision over the middle of the pie to release excess steam while baking.
Brush the pastry with egg wash and sprinkle some extra brown sugar over.
Place in the oven and bake for 40-50 minutes until golden brown colour. Remove the pie from the oven and set aside for 20 minutes to cool.
Serve with your favourite ice-cream, custard, or fresh cream.