Preheat the oven to 350 degrees.
In a large bowl, cream the butter, lemon zest and sugar until fluffy.
Add the egg and vanilla to the creamed butter and whisk until combined.
In a separate mixing bowl, whisk together two cups of the flour, 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 just until the ingredients are well incorporated.
Toss the blueberries with the remaining tablespoon of flour.
Turn off mixer. Gently fold in the blueberries by hand with a spatula.
Line a muffin tin with muffin liners. Spray the liners with cooking spray.
Fill the muffin liners almost to the top. I like to use an ice cream scoop for this. I tend to leave a 1/4-inch border around the top of the liner. The lemon blueberry muffins will rise during baking, but not so much that you risk them oozing out of the pan.
Sprinkle the top of each muffin with 1/2 a teaspoon of turbinado sugar. I love this addition because it gives the muffins a nice, sweet, crunchy topping.
Bake the muffins for 30 minutes or until the tops are golden and a toothpick inserted near the center comes out clean.
Remove the muffins from oven.
Allow the muffins to cool in the muffin tins for five minutes before removing them to finish cooling on a baking rack.