Position a rack in the center of the oven and preheat to 375 degrees . Roll out the piecrusts into two 12-inch rounds. Fit 1 round in a 9-inch pie plate. Refrigerate the prepared pie plate and the second crust until ready to fill.
Peel, core and cut the apples into 3/8-inch-thick slices. In a large bowl, toss together the apples, sugar, cornstarch, mulling spices and salt. Spoon the mixture into the prepared piecrust, pouring any juices on top. Dot with the butter and cover with the second piecrust. Crimp the edges of the 2 crusts together. Brush the top of the pie lightly with the egg white, sprinkle with a little sugar and cut 3 vents in the top.
Line a baking sheet with foil. Place the pie on top and bake until the top is golden and the filling is simmering, about 50 minutes.