Put the sliced, pitted nectarines in a big bowl. Add the flour, sugar, lemon and nutmeg. Stir til just combined.
Roll out the bottom crust and place in 9-inch pie pan. Add the fruit filling. Roll out the top crust and place it on top of the filling. Seal and crimp the edges of the pie. Put the pie in the freezer to chill while the oven is preheating.
Preheat the oven to 425. Give it at least 20-25 minutes, and preferably use an oven thermometer, to be sure it has come all the way up to 425.
Take the chilled pie from the freezer and cut a few vents in the top crust. Brush egg white lightly over the top crust and edges. Sprinkle sugar over the top (if you like). Place the pie on a parchment-lined baking sheet.
Bake in the lower third of the oven at 425 for 20 minutes, then at 375 for another 45-55 minutes, until the crust is deep golden brown.