Preheat oven to 350 degrees F.
Mix the flour with 1 teaspoon salt and baking powder in a large bowl.
Cut the butter into small chunks and add to the bowl.
Add water and mix well until have a firm rough dough.
Press the dough into a circle and wrap in plastic and leave to rest for minimum 30 minutes in the fridge.
Take out dough from the fridge and form 2 balls.
Roll into a big circle.
Place in pan and flute the edges, spread your pie filling over it.
Roll out another sheet of pie dough and lay it on top of the pan, crimping the edges to seal.
Whisk the remaining egg white and brush over the top of the pie.
Bake around 35 to 45 minutes until golden and cooked through.