Preheat oven to 350 degrees. Cream butter, lemon zest and 3/4 cup + 1 Tablespoon of the sugar together. Beat until creamy and fluffy. Add egg and vanilla and beat until combined.

Meanwhile, toss the blueberries with 1/4 cup of the flour. Set aside.

Whisk together the remaining flour, baking powder and salt together in a seperate bowl. Slowly add flour mixture to wet mixture, alternating with the buttermilk. Fold in blueberries.

Grease a 9x9 inch square pan with non-stick spray. Spread batter into pan (batter will be thick).

Sprinkle the remaining tablespoon of sugar evenly over the top of batter.

Bake for 35-40 minutes, or until a toothpick inserted comes out clean. Let cool 15 minutes before serving.