Precook the juicy, tart blackberry filling before pouring it in the crust. The streusel topping becomes a crunchy sugar-pecan crown.
Prepare Pastry for Single-Crust Pie. On a lightly floured surface, use your hands to slightly flatten dough. Roll dough from center to edge into a circle about 12 inches in diameter. To transfer pastry, wrap it around the rolling pin. Unroll pastry into a 9-inch pie plate. Ease pastry into pie plate, being careful not to stretch pastry. Trim pastry to 1/2 inch beyond edge of pie plate. Fold under extra pastry. Crimp edge as desired. Do not prick pastry. Line the pastry with a double thickness of heavy foil. Bake the pastry in a 450 degree F oven for 8 minutes. Remove the foil. Bake for 4 to 5 minutes more or until the pastry is set and dry. Reduce the oven temperature to 375 degree F.
Meanwhile, in a medium saucepan, combine the blackberries, sugar, tapioca, and cinnamon. Cook and stir over medium heat until mixture starts to bubble. Reduce heat and simmer the berry filling, uncovered, for 10 minutes, stirring the mixture frequently.
Pour the berry filling into the prepared piecrust. Top with the Pecan Streusel Topping.
Bake the pie in the 375 degree F oven for 25 to 30 minutes or until the crust and topping turn golden. Makes 8 servings.