I can't really provide a good recipe for this because it was a bit ad hoc I have to say. I had some leftover shortcrust pastry in the freezer, which I got out to defrost the night before I started baking.
When the pastry was defrosted, I rolled it out as thin as I dared - thin pastry is the best of pastry. None of this fat, soggy bottomed, raw crappy pastry which it can be so easy to do. Thin and very, very short is the only way to go. I cut the pastry I had rolled into two, and freehand, using an image pulled up on my iPad as a guide, cut the pastry into the shape of Pi. Twice. One for the bottom and one for the top. I tried to get them as lined up as possible.
I now peeleed 3 small apples and sliced them extremely thinly. The key to a good apple pie filling is to toss the apples liberally in cinnamon and brown sugar - this is what makes them scrummy.
Laying the thin slices of apple on the pi shaped pastry bottom, I very carefully arranged the slices to cover the whole pi shape. Then, covering this, I placed the second pi shape on top and using a fork, I crimped the edges to secure the filling inside the pastry. I then cut out "3.14" out of pastry and whilst egg washing the whole top of the pi, placed these on as decoration.
Top Tip: sprinkle the top of the pi with caster sugar to give it a caramalised, crunchy top.
Bake this in an oven at 180 degress for about 30 minutes until golden brown and serve with a nice fresh brew, deeeeeeeeeeeelish.