In a very large bowl stir together brown sugar, flour and salt. Add apple slices and any juices, stir to coat. Transfer to pastry lined pie plate. On lightly floured surface roll remaining dough to 14" circle and place on top of fruit filling. Cut clits for steam to escape. Trim crust to 1/2" beyond edge of pie plate. Fold top pastry edge under bottom pastry, crimp edge. Brust top with mixture of beaten egg and water. Cover edge of pie with foil to prevent overbrowning.