Stir the blackberry mixture again to make sure that everything is well distributed and the juices are evenly coating the berries. Transfer the blackberries and all the accumulated juices from the bowl to the pie dish with the rolled out bottom pie crust, spreading the filling out into an even layer. Set the filled pie aside while you prepare the top crust.
Roll out the top pie crust: Place the second dough disk onto a lightly floured work surface. Roll it out into a circle about 12 inches in diameter, turning the dough slightly as you go to maintain a round shape and even thickness. To make a lattice top crust, use a sharp knife, pizza cutter or pastry wheel to cut the dough into even ½-inch wide strips.
Using every other strip, arrange half of them going in one direction across the top of the pie, spacing them slightly apart. Then weave the remaining strips perpendicularly through the first set, lifting and folding back the initial strips as needed to create an over-under woven pattern. (If you prefer a solid top crust instead of a lattice, simply place the rolled out dough over the filling and gently press it into place. Use a sharp knife to cut a few slits in the center of the crust to allow steam to escape during baking.)
Trim the overhanging edges of the pie crust so that about a ½-inch of dough extends beyond the edge of the pie dish. Fold the overhanging dough underneath itself to seal the edges and create a thicker border. Then use your fingers to flute the edge or press with a fork to crimp, depending on your desired finish.