Instructions

Make the filling: 

1. Stir the blueberries, sugar, flour, cornstarch, cinnamon, lemon juice, and lemon zest together in a large bowl. Mix together until it’s no longer dry and powdery; burst a few blueberries if necessary to moisten. Set filling aside as the oven preheats. Filling can be covered and refrigerated for up to 24 hours if needed.
2. Adjust the oven rack to the lower third position and preheat to 425°F. Place baking sheet on the bottom oven rack to catch any blueberry juices.
3. If using homemade crust, roll out 1/2 of your chilled pie dough (keep the other half chilled) into a 12-inch diameter circle. Carefully place the dough into a 9-inch round pie dish. Tuck it in with your fingers, making sure it is smooth. 
4. Pour and spread the filling evenly into pie dish. Dot the pieces of butter on top of the filling. Set aside at room temperature or in the refrigerator as you assemble the top pie crust.

Arrange the lattice:

1. Use the other half of your dough and roll it into another 12 inch circle. Using a pastry wheel, sharp knife, or pizza cutter, cut 1 inch strips of dough.
2. Carefully thread the strips over and under one another, pulling back strips as necessary to weave. Press the edges of the strips into the bottom pie crust edges to seal. Use a small paring knife to trim off excess dough. Flute or crimp the pie crust edges with a fork.
3. Lightly brush the top of the pie crust with the egg wash. Sprinkle the top with coarse sugar, if using.
4. Bake the pie at 425°F for 25 minutes; then, keeping the pie in the oven, reduce the oven temperature down to 375°F. Place a pie crust shield (aluminum foil) on the edges to prevent them from over-browning. Continue baking the pie until the filling’s juices are bubbling everywhere, including in the center, 40–50 more minutes. This sounds like a long time, but under-baking the pie means a soupy filling with paste-like flour and cornstarch chunks.
5. Remove pie from the oven, place on a cooling rack, and cool for at least 4 hours before slicing and serving. Filling will be too juicy if the pie is warm when you slice it.
6. Cover leftovers tightly and store in the refrigerator for up to 5 days.