Preheat oven to 375 degrees. Line a large baking sheet with foil and lightly flour.
Place the piecrust atop the foil-lined baking sheet, and roll pastry to a 14 x 11-inch oval. In a large mixing bowl stir together sugar, flour and nutmeg. Stir in peaches and lemon juice. Spoon peach mixture onto crust, leaving a 2-inch border.
Fold pastry border up and over peaches, folding edges gently as needed. Combine egg and water; brush on top and sides of crust.
Bake in preheated oven for 40 to 45 minutes or till crust is golden. If necessary, cover top crust with foil for last 10 to 15 minutes of baking to prevent over browning. Cool for 10 minutes on the baking sheet. Dust edges with powdered sugar, if desired Serve with sweetened whipped cream. Makes 8 servings. Enjoy!