1. Prepare the Pie Crust: Roll out one of the pie crusts on a lightly floured surface to fit a 9-inch pie dish. Place the crust in the pie dish and press down slightly on the bottom and up the sides.
2. Mix the Filling: In a large bowl, combine blueberries, sugar, lemon zest, flour, and salt. Gently toss until the blueberries are well coated.
3. Fill the Pie: Pour the blueberry mixture into the crust-lined pie dish. Dot the top with pieces of butter.
4. Top Crust: Roll out the second crust and place over the filling. Trim excess dough, and crimp the edges to seal. Cut slits in the top crust to allow steam to escape. Brush the crust with the beaten egg.
5. Bake: Preheat your oven to 425 degrees Fahrenheit (220 degrees Celsius). Bake the pie for 15 minutes, then reduce the temperature to 375 degrees Fahrenheit (190 degrees Celsius) and continue baking for another 25-30 minutes or until the crust is golden and the filling is bubbly.
6. Cool: Allow the pie to cool on a wire rack for at least 2 hours to set the filling before slicing.

Notes

If using frozen blueberries, ensure they are completely thawed and drained to avoid excess liquid in your pie.

For a decorative touch, you can use cookie cutters to make shapes out of extra pie dough for the top crust.