Preheat to 400Â°F. Butter and flour a 9-inch round cake pan.
In a bowl, combine the flour, baking powder, baking soda, and salt. Whisk together, and set aside.
In the bowl of a standard electric mixer, beat together the butter and 2/3 cup of sugar at medium speed until light and fluffy. Beat in the vanilla, followed by the egg, beating well after each addition.
Reduce the mixer speed to low, and add the flour mixture in three batches, alternating with the buttermilk (beginning and ending with flour), and mix until just combined. Do not over mix. Gently fold in 1/4 cup of blueberries.
Spoon the batter into the cake pan, and smooth the top with a rubber spatula. Gently scatter the remaining blueberries over the top of the cake, and sprinkle with the remaining 1 tablespoon of sugar.
Bake until cake is golden and a toothpick inserted into center of the cake comes out clean, 25 to 30 minutes. Cool in pan 10 minutes before transferring the cake to a rack to cool completely. Invert the cake onto a plate before serving.