Preheat the oven to 375F/190C.
Roll out the dough on a lightly floured surface into a rectangle. If you like, you can leave as one large piece (around 15x11in, 38x28cm) and fold over the top, but I find two smaller pieces slightly easier to work with (this is what I show in the video). Once you have partly rolled the dough, divide roughly in half and roll each half out further. Roll one piece for the base to around 8x11in (20x28cm) and the piece for the top to around 7x10in (18x25cm). Slightly smaller with a thicker filling is also fine.
Line a baking sheet with parchment and place the slightly larger base piece of pastry on top. If needed, slightly trim the edges to be move even - you can use the trimmed pieces to decorate the top.
Top the pastry with the filling mixture, leaving an edge around the outside with no filling on it of around ⅔in (2cm). Try to make the filling relatively even and gently flattened on top. Place the other piece of pastry over the top of the filling and gently stretch the pastry over the filling so that it joins with the pastry below.
Working from one corner, crimp the edges of the pastry by gently pulling and folding it in on itself a little at a time (see video). If you are unsure about crimping, you could also just fold over the edge and press to seal with a fork, but crimping is a little prettier.
Cut a small hole in the middle of the pastry to form a vent for steam. If you have scraps of trimmed pastry, roll these out thinly, cut into strips and use these to decorate the top of the pie.
Brush the pie all over with egg wash (lightly beaten egg) then bake for around 40 minutes until the pastry is golden. Allow to cool slightly and enjoy either warm or at room temperature.