In a medium bowl, use a fork to combine flour, sugar, cinnamon and butter. Mix until crumbly.
Place one pie crust into a 9 inch pie plate. Scoop in one layer of peaches. Top with some of the crumbly sugar mixture. Layer more peaches and more crumbles. Continue until you've used up all of your peaches and crumbles. Top the pie with your 2nd pie crust, as desired. (I cut mine into strips and created a lattice topping. If you'd like to cover the pie completely with the 2nd crust, just be sure to cut a few slits into the top crust to give that crust a chance to breathe while baking.) Crimp the edges decoratively.
Brush the top with the egg wash, and sprinkle with coarse sugar if you wish.
Bake on the center rack in the oven for 1 hour to 1½ hours. I start checking on my pie at 45 minutes, just to make sure the crust isn't browning too quickly and all looks good. Then I check every 15 minutes until I'm satisfied that it's done. Mine took an hour and 15 minutes, and it was nice and golden brown along the crust with the peach filling bubbling a bit in the center.
Cool until ready to eat. It's quite good served warm with vanilla ice cream.
Notes
This recipe is gluten free adaptable- use a gluten free pie crust, and use all-purpose GF flour in place of regular.
I like to place a large, rimmed cookie sheet on the rack underneath my baking pie just in case the juices happen to bubble over.