Preheat the oven to 350 degrees.
In a large bowl, cream butter, lemon zest and sugar until fluffy.
Combine the egg and vanilla and whisk until combined.
In a separate mixing bowl, whisk together all but 1 tablespoon of the flour and all of the baking powder and salt.
If using a stand mixer, switch to the paddle attachment. With the mixer running on low, add 1/3 of the flour mixture to the butter mixture, alternating with half of the buttermilk. Repeat, ending with the flour mixture. Continue to mix until ingredients are well incorporated.
Toss the blueberries with the remaining tablespoon of flour.
Turn off mixer. Fold in the blueberries.
Coat an 8-in. x 8-in. square baking dish with cooking spray. Pour batter into the dish and spread into an even layer.
Sprinkle the top of the batter with the turbinado sugar.
Bake for 55-65 minutes or until a toothpick inserted near the center comes out clean.
Remove from oven. Allow to cool for 15 minutes before serving.