Put the flour and butter into a large bowl. Rub the flour and butter together till it resembles breadcrumbs, using a fork or your fingers. Then mix in the granulated sugar.
In a separate bowl, whisk together the water and egg. Quickly combine the dry and wet mixtures (I used an electric hand whisk). The consistency will be slightly sticky and wet.
Wrap the pastry in film and rest it for at least 30 minutes.
Preheat the oven to 200 C / 180 C Fan / Gas 6.
In a new large bowl, mix together the golden caster sugar, cinnamon and cornflour.
Peel the apples and pat with kitchen paper (Bramley apples have more moisture than needed for the pie). Chop the apples into strips, then cut the strips into thirds (halves may be too big but up to you).
Add the apples to the sugar mixture and toss well, trying to cover all apples.
After 30 minutes has passed since resting the pastry, halve the the dough into two balls and roll each out between two pieces of cling film (using extra flour here may have the pastry too dry and too hard when baked so try not to).
Line a 23cm (9 in) pie dish (widest diameter measured) with one of the pastry rounds, then add the apple mixture. Cover all this with the second piece of pastry. Trim and seal the edges, then cut air slits on the top lid in your own design. To make sure a nice golden colour is acheived, brush over some milk on the top of the pie.
Bake the pie for 30 minutes, or until the pastry is golden brown. Remove from oven and let cool for 15 minutes before slicing and serving.