In a large bowl, beat the butter, lemon zest, and sugar together until well-combined, about 2-3 minutes on medium.
½ cup butter, 2-3 tablespoons freshly grated lemon zest, 1 cup granulated sugar
Mix in the egg and vanilla extract until well-combined.
1 large egg, 1 ½ teaspoons vanilla extract
Add the remaining flour, baking powder, and salt.
2 teaspoons baking powder, ½ teaspoon salt
Stir in just until combined. Don't overmix.
Add the buttermilk.
½ cup buttermilk
Stir in just until combined. Don't overmix.
Fold in the blueberries just until incorporated.
Pour the batter into the prepared pan.
Sprinkle with remaining sugar.
1-2 tablespoons granulated sugar
Bake for 35-50 minutes or until a toothpick inserted in the center comes out clean.
Cool 15-20 minutes before slicing and serving.
Notes
Blueberries: Be sure to wash them and then pick them over so that you don't have any smooshy or rotten blueberries in your cake.
Flour: Be sure to properly measure the flour. To properly measure the flour, sift or stir it to break it up. Lightly spoon into the measuring cup and then level off.
Butter: I use salted butter. Feel free to use unsalted if you prefer.
Buttermilk: If you don't have buttermilk, you can make a substitute with this recipe.
Room temperature: Be sure to have you butter, egg, and buttermilk at room temperature. This will help the ingredients to combine fully.