Preheat your oven to
200 °C and lightly grease your pie dish with butter. Meanwhile, take your pastry and divide it into two unequal parts - roughly ⅖ to ⅗.
Take the larger piece of pastry and roll it out to around 3 millimetres' thickness on a lightly floured work surface, making sure it is big enough to fit into your pie dish with an overhang.
To get your pastry into the pie dish, lightly roll it around your rolling pin and then unroll it across the top of the bowl, allowing it to sink into the dish.
Lightly press your pastry into place. Don't worry about any tears. You can easily just push those back together. Leave the overhanging pastry where it is for now.
Now spoon your pie filling into the dish, into the pastry case, leaving an approximate 1 centimetre gap at the top.
Now roll out your remaining pastry to around 3 millimetres' thickness and until it is big enough to cover the top of the pie filling with an overhang.
Go round the rim of your pie dish with your fingers and gently press the pastry lid and casing together, along the rim.
Now take a fork and press around the rim to create your pie crust.
Take your sharp knife and carefully go around the edge of your pie, trimming away the excess pastry.
If you want to, you can use the excess pastry to create decoration for the top of your pie lid.
Make two or three slits in the top of your pie to allow steam to escape and place your pie dish on a baking tray.
Now brush your beaten egg over the top of your pastry lid.
Cook in the centre of the oven for around 30 minutes, or until your pie is golden brown on top.
Serve immediately.