2. Set the oven at 325 degrees. Have on hand a 9-inch pie pan.
3. On a well-floured surface, roll 1 piece of dough to a 1/8-inch thickness. Lift the dough onto the rolling pin and ease it into the pie pan. Press the dough in to fit, letting the excess hang over the sides. Brush the rim of the dough with egg.
4. In a medium bowl combine the blackberries, apples, 3/4 cup of the sugar, and tapioca; mix well. Pour into the pie shell.
5. On a well-floured surface, roll the other piece of dough to a 1/8-inch thickness. Lift the dough onto the rolling pin and lay it over the fruit. Press the edges to seal them. Trim excess dough, and crimp the edges all around.
6. Bake the pie for 1 hour, or until golden brown. Remove it from the oven and sprinkle the top with the remaining 1 teaspoon sugar. Set the pie on a wire rack to cool. Serve slightly warm or at room temperature. Keri Fisher and Matty Murphy