Preheat oven to 400 degrees F. Place a baking sheet on the lower rack to catch drips.
In a large bowl, combine frozen peaches with granulated sugar, brown sugar, cornstarch, lemon juice, cinnamon, nutmeg, and salt. Stir well and let sit 10 to 15 minutes.
Line a 9-inch pie pan with one pie crust. Pour the peach filling in and dot the top with butter pieces.
Top with the second crust, either whole with slits cut or in a lattice pattern. Press and crimp the edges firmly to seal.
Brush top crust with beaten egg and sprinkle with coarse sugar if desired.
Bake at 400 degrees F for 20 minutes. Reduce heat to 375 degrees F and bake an additional 35 to 40 minutes until crust is golden brown and filling is bubbling. Cover edges loosely with foil if browning too quickly.
Cool at room temperature at least 2 hours before slicing to allow the filling to fully set.