Preheat the oven to 400 degrees F.
Place your unbaked pie crust in a pie pan. Cut off any excess dough and crimp the edges.
In a large mixing bowl, combine your sliced apples, granulated sugar, lemon juice, cinnamon, and nutmeg. Stir the apples until the spices and sugar are evenly distributed among all of the apples.
Using clean hands, arrange the apple slices in concentric, layered circles within your prepared pie crust.
In a separate bowl, combine brown sugar, flour, and cinnamon. Cut in the unsalted butter until the mixture resembles wet sand.
Spread the sugar topping evenly atop your apple pie. Cover the edges of the pie crust with aluminium foil or a pie shield.
Place your pie on a baking sheet and bake for 30-35 minutes, until the topping is golden brown and the sugar is beginning to caramelize.
Allow to cool for at least 10 minutes before slicing and serving.