Unroll piecrust; trim into 8-inch square; cut into 10 strips. Place berries in 8-inch-square baking dish; sprinkle with 2 tbsp. sugar. In small bowl, whisk cornstarch, cinnamon, salt and 1/4 cup boiling water until cornstarch dissolves; drizzle over berries. Arrange dough strips in a lattice pattern on top of berries. Brush dough with water and sprinkle with remaining 1 tsp. sugar. Bake at 375 degrees until crust is golden and filling is bubbling, about 1 hour. Let stand 15 minutes. Serve with frozen yogurt.