Whisk flour, sugar, cornmeal, baking powder, baking soda, and salt together in a large bowl.
In a separate bowl, whisk the buttermilk, butter, and vanilla together.
About a minute before the berries comes out of the oven, add wet ingredients to dry and mix till combined.
Remove the blueberries from the oven; increase heat to 425 degrees F.
Divide the dough into 9 equal pieces and place on top of the filling, spacing them at least 1/2 inch apart.
Sprinkle each mound of dough evenly with a little sugar.
Bake until the filling is bubbling and the biscuits are golden brown on top and cooked about 15-18 minutes.
Transfer to wire rack and let cool slightly; serve warm.