The crunch in this pie comes from the oatmeal topping, which turns wonderfully golden brown and crispy in the oven, which provides delectable counterpart to the softened apples in the filling as well as the flaky crust. The apples are simply tossed with lemon juice, brown sugar, and enough flour to thicken the juices that will be released during baking. This recipe calls for ready made shortcrust, which can be store-bought or your own doing.