Preheat oven to 350 degrees F and grease a 9" square baking pan with butter or non-stick cooking spray.

Using an electric mixer (either hand mixer or stand mixer fitted with the paddle attachment), cream the butter with the lemon zest and sugar until light and fluffy (you may need to stop once or twice to scrape down the sides/bottom of the bowl).

Add in the egg and vanilla and beat on medium speed until thoroughly combined and mixture is light and fluffy (again, you might need to stop once or twice to scrape down the sides/bottom of the bowl. I needed to in order for everything to mix and to get it to be light and fluffy).

In a small mixing bowl, toss the blueberries with 1/4 cup of the flour until they are all thoroughly coated.

In a separate, medium-sized mixing bowl, whisk the baking powder, salt and the remaining flour until thoroughly combined.

Alternating between the flour mixture and buttermilk, add each into the batter a little bit at a time (I end up adding in 3 installments of each), mixing well after each addition to thoroughly combine (I use my electric stand mixer fitted with the paddle attachment on stir speed for this part).

Gently fold the blueberries into the batter, then transfer batter to prepared baking dish and sprinkle 1 Tbsp. of granulated sugar over the top.

Bake in the preheated oven for ~35-45 minutes, until a toothpick inserted into the center comes out with just crumbs (no batter). Be careful not to overbake, though, or it will end up dry and no one likes dry cake.

When the cake is done, remove it from the oven and allow to cool for ~10-15 minutes before serving. (if you're like me, it will be hard to wait... the only issue if you don't wait is it will crumble quite a bit as you cut it so you won't get cleanly cut pieces. Depending on what you're making it for, though, that might not matter!)