Prepare the topping by whisking together the flour, 1/4 cup of sugar, cornmeal, baking powder, baking soda, and salt together in a large bowl.
In another bowl, whisk the buttermilk together with the cooled melted butter and vanilla until well combined. Set aside.
In a small separate dish, combine the remaining 2 teaspoons of sugar with the 1/8th teaspoon of cinnamon; mix very well. Set aside.
One minute before the blackberries come out of the oven, add the wet ingredients to the dry ingredients; stir with a rubber spatula until just combined and no dry pockets remain.
To assemble and bake, remove the blackberries from the oven; increase the oven temperature to 425 degrees.
Divide the biscuit dough into eight equal pieces and place them on top of the hot blackberry filling, spacing them 1/2 inch apart (they should not be touching).
Sprinkle the top of each biscuit with the sugar/cinnamon mixture.
Place into the oven and bake for 15-18 minutes.
Remove from the oven and place on a wire rack to cool for 20 minutes.
Serve with ice cream or whipped cream. Enjoy.