Prepare pastry and divide in half. Form each half into a ball. On a lightly floured surface, roll one ball of the pastry into a 12-inch circle. Transfer the rolled-out pastry to a 9-inch pie plate.

In large mixing bowl, stir together the sugar, tapioca, and cinnamon. Add the blackberries and apple slices. Toss gently until coated. Let stand 15 minutes.

Spoon filling into pastry-lined pie plate. Dot with butter. Trim pastry even with the edge of the pie plate. Moisten the edge of the pastry with water.

On a lightly floured surface, roll out the remaining pastry into a 12-inch circle. Cut slits in the pastry to let steam escape. Place pastry on the filling. Trim the top crust to 1/2 inch beyond edge of pie plate. Fold top pastry under bottom pastry and crimp edge. Cover edge of crust with foil to prevent overbrowning.

Bake in a 375 degree F. oven for 25 minutes. Remove foil. Bake for 20 to 25 minutes more or until the crust is golden and the filling is bubbly. Cool on a wire rack. Makes 8 servings.