Remove pie shells from the freezer and thaw for 15 minutes. Prick one of the thawed pie shells on the bottom and sides with a fork.
Meanwhile, combine apples, lemon juice, spices, and flour in a mixing bowl.
Then spoon mixture into pie shell that was pricked with the fork. Then cut slivers of butter and place on top of mixture.
Next cover with the second pie shell pinching edges together with your fingers. Cut two slits in the top of crust to allow steam to escape. Finally, brush the top with beaten egg. Place on a baking sheet as the pie may bubble over a bit and bake until crust is golden, about 50 minutes. Let cool on wire rack before serving.
I used Granny Smith apples in this recipe. They're tart and tangy. Generally, we want firm apples. Honeycrisp and Braeburn are sweeter yet firm. But, I have even used Delicious apples with this recipe.
If your frozen pie shell is broken, thaw the shell. Then dampen the crack with water, and use your finger to seal the crack together by lightly pinching and pressing the dough.
I served this pie with homemade whipped cream. You might even like to top it with a scoop of vanilla ice cream dusted with cinnamon. Or just have it plain. It's up to you.