Place the first crust on a lightly floured surface. Roll the dough out into a 12 inch circle.
Once your circle is rolled out, fold the dough in half and pick it up and place into a 9 inch pie plate. Unfold the dough and gently push the dough into the bottom and sides, working out all of the folds.
In a bowl, add in the cornstarch and sugar. Stir until incorporated.
Add the blueberries and lemon juice to a large bowl.
Pour the sugar and cornstarch mixture on top of the berries and stir until evenly distributed. Set aside and work on the second crust.
Roll the dough out into about a 12 inch circle on a lightly floured surface.
Cut 1 inch wide strips all the way across the circle with a pizza cutter.
Stir the blueberry filling once again until coated with the sugar and cornstarch and then pour into the pie crust.
In a small bowl, add in the egg and water. Whisk until thoroughly combined.
Use a pastry brush and brush the egg wash on the edges of the pie crust.
Start placing strips of pie dough on the blueberry filling. I always grab the longest pieces and place them in the middle to form a plus sign. Then I work my way outwards with the strips of pie crust interlacing the pieces.
To weave the pieces, fold every other piece of crust back and then lay the new strip on top of the remaining pieces. Unfold the strips and fold the ones that are now underneath the strip you just placed down. Repeat until the pie crust is covering the top of the pie.
Gently press down the pieces on the edge of the crust and cut off any dough that hangs farther than ½ inch off the edge of the crust.
Fold the ½ inch overhang underneath the bottom crust and crimp the edges.
Place in the preheated oven for 1 hour to 1 hour 10 minutes until the filling appears thick as it bubbles around the lattice crust.
Remove from the oven and allow to cool completely. Slice and serve.
Cover with plastic wrap and store in the refrigerator.