Preheat the oven to 350°F (177°C). Roll out the pie crust and place it into a 9-inch pie dish, then set it aside.
In a large bowl, combine the sliced Granny Smith apples, granulated sugar, cornstarch, lemon juice, cinnamon, and vanilla extract. Mix until the apples are evenly coated. Allow to sit for 10 minutes.
In a separate bowl, mix together the flour, brown sugar, and cinnamon. Stir in the melted butter until the mixture resembles coarse crumbs.
Add the apple mixture into the prepared pie crust, leaving the juices in the bowl. Sprinkle the crumble evenly over the apple filling.
Bake the pie for 35 minutes, or until the apples are tender and the crumble is golden brown. Let it cool for at least 1 hour before serving.
Notes
Tips for slicing apples: For even baking, try to slice your apples to a consistent thickness. Thin apple slices ensure that they cook evenly and soften to the right texture without becoming mushy. Mushy apples will create a soggy bottom on your pie, and we don't want that!Adjusting for sweetness: Taste your apples before baking. If your apples are very tart, you can increase the sugar slightly. Alternatively, for a less sweet pie, reduce the sugar by 1-2 tablespoons.Be patient! It's important to allow the pie to cool for at least 1 hour before serving. It gives the filling time to set, so that it won’t be too runny when you slice into it.Storing leftovers: Store leftover pie at room temperature for up to 2 days, or store in the refrigerator for up to 4 days. To reheat, warm it in a 350°F (177°C) oven for 10-15 minutes.Freezing instructions: This classic apple pie can also be frozen! Freeze it either before or after baking. To freeze before baking, assemble the pie shell and freeze. Bake straight from frozen, adding 10-15 minutes to the baking time. If you freeze after baking, then just let the pie cool completely before wrapping and freezing.