Combine berries, sugar, and tapioca in a medium bowl; let stand 15 minutes or until tapioca softens. Spoon berry mixture into a buttered 11- x 7-inch baking dish, and dot with 1 tablespoon butter. Bake at 400° for 10 minutes or until berries are hot.
Combine flour and next 3 ingredients in a medium bowl. Cut 1/2 cup butter into flour mixture with a pastry blender until crumbly; add buttermilk, stirring just until dry ingredients are moistened. Gather dough into a ball. Turn dough out onto a lightly floured surface; knead 5 or 6 times. Pat or roll dough into an 11- x 7-inch rectangle.
Carefully place pastry over hot berries. Brush top of pastry with whipping cream, and sprinkle with sugar. Bake at 400° for 15 to 20 minutes or until top is lightly browned. Serve with sweetened whipped cream or vanilla ice cream, if desired.