Preheat oven to 350°. Combine blueberries, lemon juice and lemon zest. In another bowl, combine sugar, tapioca, cornstarch and cinnamon. Add to berries; toss gently to coat., On a lightly floured surface, roll half the pie dough to a 1/8-in.-thick circle; transfer to a 9-in. pie plate. Trim crust to 1/2 in. beyond rim of plate. Add blueberry mixture. Dot with butter. , Roll remaining dough to a 1/8-in.-thick circle; cut into 1-in.-wide strips. Arrange over filling in a lattice pattern. Trim and seal strips to edge of bottom crust; flute edge. Whisk egg and milk; brush over crust. If desired, sprinkle with coarse sugar., Bake 30 minutes. Cover edge loosely with foil. Bake until crust is golden brown and berries have burst, about 30-35 minutes more. Cool on a wire rack.