Preheat the oven to 350 degrees. Cream butter with lemon zest and 3/4 cup and 2 Tbsp of sugar until light and fluffy. Add the egg and vanilla and beat until combined. Meanwhile, toss the blueberries with 1/4 cup of flour. Then whisk together the remaining flour, baking powder, and salt. Add the flour mixture to the batter a little at a time, alternating with the buttermilk. Fold in the blueberries. Grease a 9 inch square baking pan with butter or coat with non-stick spray. Spread batter into pan. Sprinkle batter with remaining tablespoon of sugar. Bake for 35 minutes. Check with a toothpick to make sure it is done. If necessary, return pan to oven for a couple of more minutes. Let cool at least 15 minutes before serving.