Once the dough has chilled, remove one of the disks from the fridge & on a lightly floured surface, roll it out into a roughly 12-inch circle that is about ΒΌ-inch thick. Carefully press the dough into your pie dish/tart tin & store in the fridge while you prepared the filling. (Think of the flakes.)
Remove the second disk from the fridge & roll out into a circle roughly 12-inches. Place on a sheet pan & leave to chill in the fridge.
Preheat the oven to 200C.
Now, the filling. In a large bowl, gently stir together the peaches, caster sugar, cornflour, & lemon juice.
Fill the prepared pie shell with the filling & cover with the second prepared crust (or make make this crust into a lattice topping. I watched a tutorial on youtube), crimp the edges together, and slide the whole thing into the freezer for at least 15-minutes. (I believe this was crucial to my success.)
When ready to bake, brush the top of the pie with the beaten egg yolk and sprinkle with some sugar before baking in the preheated oven for 40-50 minutes, or until the juices are bubbling & the crust is a deep golden brown.
Leave the pie to cool & serve warm with some lightly whipped cream.