First, pat the fresh blueberries dry; this prevents them from sinking to the bottom of your cake. In a medium bowl, whisk together the all-purpose flour, baking powder, and kosher salt. Then, in a separate small bowl, gently toss the dried blueberries with 1/4 cup of the flour mixture. This light coating also helps keep them suspended evenly throughout the batter.

Preheat your oven to 350°F and grease an 8- or 9-inch baking pan; this ensures easy release later. In a large mixing bowl, cream together the softened unsalted butter, lemon zest, and 1 cup of sugar (reserving 1 tablespoon for later). Once light and fluffy, beat in the room temperature egg and vanilla extract until well combined, scraping down the sides as needed. I find that using room temperature ingredients emulsifies better, leading to a smoother batter.

Alternately add the prepared flour mixture and buttermilk to the creamed butter mixture, starting and ending with the flour. Mix on low speed until just combined, being careful not to overmix, as overmixing can develop gluten and make your cake tough. Gently fold in the flour-coated blueberries until evenly distributed throughout the batter. I always fold by hand to ensure the delicate blueberries don’t get crushed.

Pour the batter into your greased baking pan and spread it evenly. Sprinkle the remaining 1 tablespoon of sugar over the top of the batter; this will create a lovely crispy crust. Bake for 35 to 45 minutes, or until a wooden skewer inserted into the center comes out clean. Once baked, let the cake cool in the pan for about 15 minutes before inverting it onto a wire rack to cool completely.