Preheat oven to 350 degrees. Butter a 2 1/2-quart baking dish; set aside.
COBBLER: In a large bowl, combine blackberries, sugar-cinnamon, and cornstarch; gently toss to coat. Pour into prepared baking dish.
TOPPING: In a separate bowl, whisk together flour sugar, baking powder, and salt. Using a pastry blender, cut the butter into the flour mixture until it resembles coarse crumbs. Stir in buttermilk just until moistened. Drop by tablespoonfuls on top of berries and sprinkle with sparkling sugar.
Bake uncovered for 30-35 minutes until golden and bubbly. Serve warm with whipped cream or ice cream if desired.