1. Cut 1 1/3 cups butter into small cubes, and chill 15 minutes. Stir together 4 cups flour and 1 1/2 tsp. salt. Cut butter into flour mixture with a pastry blender until mixture resembles small peas. Gradually stir in 1/2 cup ice water with a fork, stirring until dry ingredients are moistened and dough begins to form a ball and leaves sides of bowl, adding more ice water, 1 Tbsp. at a time, if necessary. Turn dough out onto a piece of plastic wrap; press and shape dough into 2 flat disks. Wrap each disk in plastic wrap, and chill 30 minutes to 24 hours.
2. Preheat oven to 425º. Place 1 dough disk on a lightly floured surface; sprinkle dough lightly with flour. Roll dough to about 1/4-inch thickness. Starting at 1 edge of dough, wrap dough around a rolling pin. Place rolling pin over a 9-inch pie plate, and unroll dough over pie plate. Press dough into pie plate.
3. Roll remaining dough disk to about 1/4-inch thickness on a lightly floured surface.
4. Peel peaches, and cut into 1/2-inch-thick slices; cut slices in half. Stir together brown sugar, next 3 ingredients, and remaining 1/4 cup flour in a bowl; add peaches, stirring to coat. Immediately spoon peach mixture into piecrust in pie plate, and dot with 1 1/2 Tbsp. butter. (Do not make mixture ahead or it will become too juicy.)
5. Carefully place remaining piecrust over filling; press edges of crusts together to seal. Cut off excess crust, and reserve. Crimp edges of pie. If desired, reroll excess crust to 1/4-inch thickness. Cut into 3-inch leaves using a knife. Brush top of pie with beaten egg; top with leaves. Brush leaves with egg; sprinkle with 1 1/2 Tbsp. granulated sugar. Cut 4 to 5 slits in top of pie for steam to escape.
6. Freeze pie 15 minutes. Meanwhile, heat a jelly-roll pan in oven 10 minutes. Place pie on hot jelly-roll pan.
7. Bake at 425° on lower oven rack 15 minutes. Reduce oven temperature to 375°; bake 40 minutes. Cover loosely with aluminum foil to prevent excessive browning, and bake 25 more minutes or until juices are thick and bubbly (juices will bubble through top). Transfer to a wire rack; cool 2 hours before serving.