Mix sugar, flour, cinnamon and peaches together in a large mixing bowl. Add 2 Tbsp of water if using fresh peaches. Cook over moderate heat, stirring constantly, until mixture thickens and boils.
Pour into pastry lined 9 inch pan and dot with butter. Place 2nd pastry over pan. Trim and crimp the 2 pastries together and add slits in the top. Cover edge of crust with foil until the last 10 minutes of baking.
Bake at 425˚ for 35 to 45 minutes or until crust golden brown and juices are bubbling through the slits.