Preheat oven to 425 degrees F. Coat an 8-inch round cake pan with cooking spray; set aside.
In a large bowl, combine the cornmeal, flour, baking powder, salt,and 1/4 cup sugar.
Make a well in center of mixture. In separate bowl, combine buttermilk and next 3 ingredients. Add to dry ingredients, stirring until dry ingredients are moistened.
Pour batter into prepared cake pan. Top with blueberries.
Combine remaining 2 tablespoons sugar and cinnamon; sprinkle evenly over blueberries. Bake at 425 degrees for 20 minutes or until a wooden pick inserted in center comes out clean. Let cool 10 minutes in pan on a wire rack. Sift powdered sugar evenly over cake.