1. Preheat oven to 450 degrees
2. In a large bowl combine the sliced peaches and lemon juice, gently toss together. Place the sliced peaches in a colander to drain. Don't skip this step, this eliminates some of the juice so your pie won't be soupy after it's cut. When I drained my peaches I collected almost a 1/4 cup of juice. Drain peaches about 10 - 15 minutes. Place drained peaches in a large bowl.
3. Place one homemade or pre-made pie crust in the bottom of a 9 inch pie pan. Brush the pie crust (bottom and sides) with a little of the beaten egg. This keeps the crust from getting soggy. Keep the rest of the beaten egg to brush on the top crust.
4. In a medium size bowl combine the flour,cornstarch,sugars,cinnamon and salt. Stir to combine. Pour the flour mixture over the drained peaches and gently fold them together.
5. Pour peaches into the bottom pie crust and dot with butter. Place the top crust over the peaches and flute edges. Brush with the rest of the beaten egg and cut 4 slits in the top crust to vent steam. You can sprinkle sugar on top of the crust for decoration if you like. Place pie on a baking sheet, I always do this so there's no chance of spills in the oven.
6. Bake the pie at 450 degrees for 10 minutes, reduce heat to 350 degrees. Bake an additional 30-35 minutes until crust is brown and juices bubble up through the slits. If your pie edges brown to quickly, cover the edges with strips of aluminum foil and continue baking. After the pie has cooled completely, refrigerate it for a couple hours before cutting.