This dessert sandwiches juicy and sweet berries between a streusel top and a flaky pastry crust.
For pastry, stir together the 2 cups flour and the salt. Using a pastry blender, cut in the 2/3 cup butter until pieces are pea size. Sprinkle 1 tablespoon of the water over part of mixture; gently toss with a fork and push to side of bowl. Repeat until all is moistened.
Divide dough into 6 portions. Form each portion into a ball. On a lightly floured surface, use your hands to slightly flatten dough. Roll each portion of dough to an 8-inch circle.
Transfer pastry to six 10-ounce custard cups or oven-safe bowls or 6 individual pie pans. Ease pastry into baking containers, being careful not to stretch pastry. Trim the pastry to 1/2 inch beyond the edge. Fold under extra pastry. Crimp the edge as you like. Place baking containers on a baking sheet.
For filling, in a large bowl, stir together granulated sugar, tapioca, and the 3 tablespoons flour. Add the 6 cups blackberries. Let mixture stand 15 to 30 minutes or until berries are partially thawed, but still icy. Transfer berry mixture to the pastry-lined baking containers.
For topping, in a medium bowl, combine the 1 cup flour, the brown sugar, and cinnamon. Using a pastry blender, cut in the 1/2 cup butter until crumbly. Sprinkle over filling. Bake in a 375 degree F oven about 35 minutes or until pastry is golden. Cool slightly on a wire rack. Serve warm. Dollop with whipped cream and garnish each with a berry and mint, if you like. Makes 6 servings.