For this recipe you'll need to prepare the sourdough pie crust in advance. When you are ready to assemble the apple pie, take the sourdough pie crust out of the fridge. Separate the pastry into two portions, one for the top and one for the bottom.
Roll the first portion out until it's large enough to fit your pie dish. For this recipe I used a 1.47Q or 1.4L pie dish. Place the rolled out pastry into the pie dish and gently ease the pastry into the base (don't stretch it). Ensure there is a little overhang so you can join the top crust to the bottom crust and then cut any excess off.
Pour in the apple mixture you prepared earlier ensuring it's packed in as the filling will sink down as it bakes.
Now roll out the second portion of pastry and place it over the top of the pie, cutting off any excess pastry.
Use a fork, or your fingers, to crimp the top and bottom crust together.
Cut a small vent in the centre of the pie with a sharp knife.
Mix the egg and water together and generously brush the top of the pie all over with the egg wash.
If you haven't already preheated the oven, pop the pie in the fridge while you preheat the oven to 390F (200C).
When the oven is preheated, place the pie into the oven at 390F (200C) for around 30 minutes. After this time, reduce the temp to 350C (175C) and bake for a further 45 minutes or until the crust is golden and filling is bubbling (you'll be able to see it through the vent you cut in the top).See notes for further info on using a pie shield. Once the pie is golden and baked through, take it out of the oven and allow it to sit for around 4 hours before slicing into it. This will ensure the sauce thickens and you don't get a soggy pie.