Fit 1 piecrust into a 9-inch pieplate according to package directions; chill.
Stir together 3/4 cup sugar, cornstarch, and cinnamon in a large bowl; add apple and next 3 ingredients, tossing well. Spoon into prepared piecrust; dot with butter.
Unfold another piecrust, and press out fold lines; transfer to top of pie. Fold edges under, and seal by pressing with tines of a fork. Cut an "X" in top of crust for steam to escape.
Unfold remaining piecrust, and press out fold lines. Cut with a tree-shaped cutter; arrange trees on top of pie.
Whisk together egg and 1 tablespoon water; brush evenly over top of pie. Sprinkle with remaining 1/4 cup sugar.
Bake at 400° for 20 minutes; reduce temperature to 350°, and bake 40 minutes. Serve warm, or cool on a wire rack. (To reheat, cover loosely with aluminum foil, and bake at 350° for 20 to 25 minutes.) Serve with vanilla ice cream, if desired.