Fill pie crust generously with apple slices. In a bowl, combine sugar and cinnamon. Sprinkle over apples. Alternatively, the sugar and cinnamon can be stirred in with the apples before filling the crust.
In another bowl, mix together the flour and sugar. Cut in the butter until crumbly. Sprinkle over apples in crust.
Bake in the preheated oven for about 40 minutes, until crumb topping turns a light golden brown. Cool before slicing and serving.