Preheat oven to 350º F and lightly grease a 9×5-inch baking dish with butter or non-stick spray.
Toss blueberries in 1/4 cup flour until coated, then set aside.
In a large bowl or mixer, cream together butter, sugar and lemon zest for 3-5 minutes, or until fluffy, and lightened in color.
Beat in egg, then, once fully incorporated, add in vanilla extract.
In a separate bowl, whisk together remaining flour, baking powder, salt and cinnamon, if using.
Alternating between the flour mixture and the buttermilk, add both to the batter, beginning and ending with the dry ingredients.Alternating between the flour mixture and the buttermilk, add both to the batter, beginning and ending with the dry ingredients.
Fold floured blueberries into the batter, then pour it into greased baking dish. Top with 1 tablespoons sugar, then place dish in oven.
Bake for 40-50 minutes, or until toothpick inserted in center comes out clean.
Remove from oven and transfer to a wire rack to cool (at least 15 minutes).
