Preheat the oven to 400F degrees.
Add the blueberries, sugar, cornstarch, lemon juice and cinnamon to a large bowl.
Stir the mixture so the blueberries are evenly coated.
On a well-floured surface using a floured rolling pin, roll out one disc of pie dough into a circle about 12-inches in diameter.
Transfer the dough to a 9-inch pie plate.
In a small bowl whisk together the egg and water.
Brush the bottom of the pie dough with the egg wash.
Using a slotted spoon, spoon the blueberry mixture into the pie. Do not add the liquid to the bottom of the bowl. Place the pie in the fridge.
Re-flour your work surface and rolling pin, then roll out the second disc of pie dough into a circle about 10 inches in diameter. Cut into strips about ½- ¾ inches thick.
Place 4-5 strips vertically over the pie. Then weave 4-5 strips horizontally, going over and under each of the vertical strips, alternating between which strip goes over and under.
Cut the excess off the edges.
Fold the edges over and crimp with your fingers, or press down with the tines of a fork.
Brush the top of the pie with the egg wash.
Place the pie in the fridge for 10 minutes before baking.
Bake in the preheated oven for 50-60 minutes. Use a pie shield to prevent the edges from burning. Or after about 30 minutes of baking, tent a piece of aluminum foil overtop to prevent burning.
Cool fully before slicing and serving.