Put the slices of butter on top of the pie filling, placing them as evenly as possible.
Carefully remove the pie crust from the pan it is in, and place it carefully on top of the pie filling and butter. You will need to cut off the edges that hang over and make them fit on the square pan.
Sprinkle liberally with cinnamon and sugar. Bake for about 20 to 25 minutes, until pie crust is lightly browned.