Preheat oven to 350°F (175°C). Grease a 9×9-inch baking dish.
In a large bowl, beat together the butter, sugar, and lemon zest until light and fluffy.
Add the egg and vanilla extract. Mix until smooth.
In a separate bowl, whisk together 1¾ cups flour, baking powder, and salt.
Gradually add the dry ingredients to the butter mixture, alternating with the buttermilk. Mix just until combined.
Toss the blueberries with the remaining ¼ cup flour to coat. Gently fold them into the batter.
Spread the batter evenly into the prepared baking dish and sprinkle a little sugar over the top.
Bake for 40 minutes, or until a toothpick inserted in the center comes out clean.
Enjoy!