Preheat oven to 350 degrees. Grease an 8 or 9-inch square pan; set aside.

With an electric mixer, beat the butter, lemon zest and 1 cup of sugar until light and fluffy.

Add the egg and vanilla and mix to combine. In a medium bowl, toss the blueberries with 1 tablespoon of flour; set aside.

In another medium bowl, whisk together 1 cup flour, the baking powder and the salt. Stir half the flour mixture into the the butter mixture, followed by all of the buttermilk.

Add the remaining flour mixture and stir until just combined. Gently fold in the blueberries.

Spread the batter into the prepared pan. Sprinkle the top evenly with the remaining 2 tablespoons of sugar. Bake for 40-45 minutes, or until a toothpick inserted in the center comes out clean.

Let cool on a wire rack for 15-20 minutes before slicing and serving.