Heat oven to 350 degrees and place a rack in the upper third of the oven. Grease a 9-by-5-inch loaf pan and line with a strip of parchment paper that hangs over the long sides to create a sling. Lightly grease the inside of the pan and set aside.

In a large bowl, combine sugar and lemon zest together and rub until the zest is fully incorporated, about 1 minute. Add cornmeal, flour, salt, baking powder and baking soda. Whisk until fully blended.

To the bowl of dry ingredients, add the chilled butter, pressing and rubbing the butter into the mixture with your fingers until a coarse, sand-like texture has been achieved, about 5 minutes.

Add the whole eggs and egg yolk, mixing with a rubber spatula until fully incorporated and making sure any stray butter pieces are fully blended in, about 2 minutes. Fold in the vanilla extract and sour cream until no streaks remain and a fluffy batter forms. Fold 1½ cups of the blueberries (reserving ½ cup for the topping) into the batter.

Pour the batter into the prepared pan and run a butter knife lengthwise in a shallow line down the middle of the batter to help it bake more evenly. Sprinkle with the remaining ½ cup blueberries.

Bake for 45 minutes, then rotate the pan and bake for another 30 to 35 minutes, until golden brown and a toothpick inserted in the middle comes out clean. Remove the cake from the oven and rest in the pan on a cooling rack for 1 hour, then remove it from the pan and let it cool another hour before glazing.

When the cake is completely cooled, combine the powdered sugar with the lemon juice in a medium bowl and whisk until a smooth yet thick glaze forms, adjusting with a splash of water if needed. Pour half of the glaze over the top of the cake, allowing some to drip over the side. Carefully pour the rest of the glaze on top, filling in any uncoated spots. Let the glaze set for at least 30 minutes before slicing.