Preheat the oven to 375 degrees. Line a pie plate with one pastry crust. Place the pie plate on a rimmed baking sheet to catch any drips.
In a mixing bowl, combine the blueberries, sugar, cornstarch, and lemon juice. Stir gently to combine. Spoon this mixture into the prepared pie plate.
Dot the surface of the berry mixture with the butter cubes.
Fit the top crust. If desired, cut shapes out of the crust and layer those across the surface of the berries.
Brush the crust with the beaten egg.
Bake for 45 minutes to 1 hour, or until the crust is golden and the filling is thick and bubbly. Cover with aluminum foil if the crust browns too quickly.
Cool the pie completely, on a rack, before serving.
Notes
Note: The pie can be frozen prior to baking. Do not allow the blueberries to thaw. Prepare it quickly.Once it is assembled, wrap it gently but firmly with heavy duty aluminum foil and store in the freezer.To bake, place the pie on a rimmed baking sheet to catch the drips. Bake at 425 for 15 minutes before reducing the heat to 375 and continuing baking until done.Promptly store leftovers in an airtight container in the refrigerator, for up to 3 days.Nutritional values are approximate and based on ⅛ the pie.