Fit one pie crust into a 9-inch pie plate and refrigerate it while preparing the filling.
Toss the apples with the sugar, flour, cinnamon, nutmeg, salt and lemon juice and mound them in the crust; dot with butter.
Cover with the second crust, crimp the edges, cut 5 vents and brush the top with the egg beaten with water.
Bake at 425°F for 20 minutes, lower the oven to 375°F and bake for 35 to 40 minutes until the crust is deep golden and the filling bubbles through the vents.
Cool for at least 3 hours, warm individual slices briefly and top each with 1/2 cup vanilla ice cream.