Remove dough from the refrigerator and let sit at room temperature until malleable. Roll ½ of chilled dough into a 12-inch circle between two pieces of heavy-duty plastic wrap. Remove top layer of plastic; invert and center dough over a 9-inch nonstick pie pan. Press crust into place, then remove remaining plastic wrap.
Toss blackberries with tapioca flour then add honey, lemon juice and orange zest. Pour into prepared pie shell.
Roll the remaining ½ of chilled dough into a 10-inch circle between two pieces of heavy-duty plastic wrap. Remove top layer of plastic; invert and center dough over filling. Press dough into place, then trim, seal and flute the edges. Cut four vents in the top dough using a decorative pattern (if desired) or create a lattice top crust.
If desired, brush top crust with an eggwash made from 1 egg whisked thoroughly with 1 Tbsp water.
Bake at 425°F for 15 minutes then reduce the heat to 350°F and continue to bake until the filling is set and beginning to bubble and the crust is golden, about 60 minutes.
