Preheat oven to 425º F (219º C).
Place bottom pie crust on greased 9-inch pie dish.
Mix berries, brown sugar, regular sugar, flour, cinnamon, and salt in large large mixing bowl.
Pour filling onto the pie crust.
Break up little pieces of butter and place on top of filling.
Top with pie crust. Fold edges back and below bottom crust so that the filling doesn’t pour out during the baking process.
Make two small cuts to form an "X" right in the middle of the top crust to let steam out during the baking process.
Mix the egg white with 1 tablespoon of water and brush on to the top of the pie.
Sprinkle a little brown sugar over the pie and put it in the oven for 35 minutes. Serve with vanilla ice-cream if you like :)