Take the pastry out of the fridge and divide it into ⅔ and ⅓.
Use the larger section (the ⅔) of the pastry to line your 25 cm (10") pie dish.
Roll the pastry out the size of 33 cm (13") Ø disc and gently transfer it to your pie dish.
Trim the edges and gently press to tuck the pastry in the cavity of the pie dish.
Fill the pastry shell with the apple and blackberry filling and spread it evenly.
Keep the pie in the fridge while preparing the lattice top.
Roll out the other piece of the dough ball into a 25cm (10") Ø disc and cut it into 10 strips using a sharp small knife.
Thread the strips over and under one another, pulling back strips as necessary to weave. Use the shorter strips for the edges and the longer ones for the middle of the pie. Trim each strip comes to the edge of the pie.
If you don't want to make a lattice top, just cover the top of the filling with the dough disc and make a small hole in the middle to let the steam out.
Crimp or pinch the outer edge to seal the top and bottom crusts together.
Egg wash the lattice top with the egg yolk using a brush.
Place the pie in preheated oven and bake for 30 minutes. Check the pie and cover the top with tin foil if it is already brown and bake it for another 15 minutes or until the filling is bubbling away.
Serve it with a dollop of ice cream, clotted cream, vanilla custard, or cream.