Heat the oven to 425°F with a rimmed sheet pan on the lower rack.
Toss the blueberries with the sugar, cornstarch, lemon zest, lemon juice and cinnamon.
Roll one dough disk into a 12-inch circle, fit it into a 9-inch plate, add the berries, and dot with butter.
Cover with the second rolled crust, trim and crimp, cut 5 vents, and brush with egg wash.
Bake for 20 minutes, lower the oven to 375°F, and bake 35 to 40 minutes more until thick bubbles rise through the center vents.
Cool for at least 3 hours before slicing.