Preheat oven to 450°F.
Using a fork, poke holes in the pie shell and bake for 6-7 minutes. Pie shell should not be browned.
After pie shells has been baked, reduce oven temperature to 350℉
In a large bowl, toss together peaches and blueberries
Fill your pie shell with the fruit mixture.
Mix egg, butter, sugar, flour, lemon zest and salt until combined then pour evenly over fruit mixture.
Place the pie back into the oven and bake for about an hour, or until filling is set.
Cool the pie to room temperature, then cover and refrigerate until custard is set and serve.