Melt butter in a skillet over medium heat. Combine cornstarch with 1/3 cup sugar; add to skillet. Stir in peaches, cinnamon and salt. Cook until mixture thickens and boils, about 25 minutes, stirring frequently. Boil for one minute; remove from heat and stir in lemon juice. Cool completely; set aside.
Cut crusts into quarters; spoon 2 tablespoons filling into the center of each quarter, leaving 3/4-inch dough uncovered on each side. Fold dough over filling; press edges together to seal.
Transfer pies to 2 ungreased baking sheets. Brush tops of pies with egg; sprinkle with remaining sugar. Cut a one-inch slit in the top of each pie.
Bake at 425 degrees for 18 to 20 minutes until golden, rotating baking sheets between upper and lower racks halfway through baking. Remove to wire racks to cool.