Start by peeling and dicing your apples. Chop to about a 2 cm dice (fairly small). Place in a saucepan with the butter and sugar and cook on a medium heat for about 5-10 minutes, until soft and golden brown. Drain off any excess caramel liquid. Let cool.
Once the apple filling is cool, preheat the oven to 200℃/180℃ fan.
Roll out the pastry, and cut into 10 rectangles: do this by cutting into 5 strips and then cut along the middle so you have 5 'pairs' of pastry sheets.
Spoon the apple mixture onto half of the pastry sheets, making sure to leave space at the edges. Press on another rectangle of pastry, and press together using a fork to form a sealed pie!
Brush with beaten egg/milk if using. Then bake for about 20 minutes, until golden! Let cool a little, best served warm!