In a medium bowl, toss the apple slices with the lemon juice. Add the granulated sugar, light brown sugar, apple pie spice and flour. Toss to combine and set aside.
Preheat the oven to 400 degrees F.
Divide the pie crust in half and roll each half into a rough circle. Place the bottom crust in a 6-inch pie dish and trim the excess dough with kitchen scissors or a small knife.
Spoon the filling into the crust, leaving the excess juices in the bowl. Mound the apples in the middle, since they cook down as they bake.
Lay the top crust over the apples and trim, leaving about a 1-inch overhang. Tuck the top crust under the bottom crust, then crimp the edges or press with a fork to seal.
Cut four 2-inch slits in the top crust. Use any leftover dough to cut decorative shapes with cookie cutters and place them on top.
Whisk the egg with 1 teaspoon water to make an egg wash. Brush it over the entire crust.
Gently cover the edges of the crust with foil or pie shield. Set the pie on a rimmed baking dish and bake on the center rack for 25 minutes. Remove the foil, rotate the pan, and bake another 30 to 35 minutes, until the crust is golden and crisp.
Transfer to a cooling rack and let cool for 2 hours. Serve.