Roll out the sourdough pie crust and place it into a 9-inch pie dish.
In a large bowl, combine fresh blueberries, sugar, flour, cornstarch, ground cinnamon, lemon juice, and lemon zest. Mix gently to coat the berries well.
Pour the blueberry mixture into the prepared pie crust.
Prepare the egg wash by whisking the egg with a splash of milk and brush it on the edges of the crust for a golden finish.
Bake the pie at 425°F (220°C) for 20 minutes, then reduce the temperature to 350°F (175°C) and bake for an additional 25-30 minutes, until the crust is golden and the filling is bubbling.
Allow the pie to cool before serving.
Notes
Use fresh ripe blueberries for the best flavor
Let the pie cool completely to allow the filling to set properly