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 about 2 cups of water (470ml) and cook on a medium heat for about 15 minutes, until soft and golden brown. Drain off the excess liquid. Let cool.
Once the apple filling is cool, preheat the oven to 400℉/200℃ and line a large baking sheet.
Roll out the pastry, and cut into 8-10 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, pressing together to keep compact - and make sure to leave a 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 if using. Sprinkle with a little extra sugar on each.
Bake for about 20 minutes, until golden! Let cool a little, best served warm!