In a large bowl mix together flour, salt, baking powder, and brown sugar.
Cut the cold butter into little cubes, about 1cm x 1cm.
Mix the cubes into the flour mixture, then with your finger tips, rub the butter and flour through your fingers until it resembles coarse meal. (You can also use a pastry blender for this. If you are doing a smaller batch, you can pulse it in the food processor)
Add the beaten egg.
Mix the vinegar into the cold water and add it a little at a time, while you are mixing with your hands, until the dough holds together. (You may not need all of the water)
Split the dough into portions (one for each pie), form each into a disk.
Wrap each in cling-film and chill in the refrigerator for about 1 hour.
Roll out and line pie plates. Chill in the fridge or freezer until ready for use. Then cook according to your pie recipe.