Bake 40 to 45 minutes or until juices bubble and crust is golden.
Cool 10 minutes before serving, or serve room temperature.
Preheat oven to 400°F.
Combine blackberries, sugar, tapioca, lemon zest and cinnamon in a large bowl. Stir gently to combine.
Arrange one pie crust in the bottom of a 9-inch pie pan. Fill with blackberry mixture and scatter butter on top. Cut a few small slits decoratively in center of remaining pie crust. Center dough over blackberries. Pinch overhanging edges together, roll under and crimp with thumb and forefinger to seal dough around edge of pan.