On a lightly floured work surface, roll out half the dough to 1/8-inch-thick circle, about 13 inches in diameter. Drape dough over a 9-inch pie pan, and transfer to refrigerator to chill for about 30 minutes.
Heat oven to 425 degrees. Whisk together egg and milk to make egg wash, and set aside. Combine blueberries, lemon juice, sugar, flour, and cinnamon, and turn onto chilled bottom crust. Dot with butter. Roll out the remaining dough to the same size and thickness. Brush the rim of the crust with the egg wash, place the other piece of dough on top, trim to 1/2 inch over edge of pan, and crimp the edges with a fork or your fingers. Transfer the pie to the refrigerator to chill until firm, about 30 minutes. Brush with the egg wash, and bake for 20 minutes. Reduce heat to 350 degrees and bake for 30 to 40 minutes more or until juices are bubbling. Let cool before serving.