Preheat your oven to 350°F. Grease a 13"x9" baking pan with cooking spray and line it with parchment paper, leaving an overhang on both long sides.
In a large bowl, whisk together the flour, salt, and baking soda.
In another large bowl, use a handheld mixer or stand mixer to beat the butter, lemon zest, and 2 cups of granulated sugar until fluffy.
Add the eggs one at a time, beating well after each addition, then add the vanilla extract.
Gradually add the dry ingredients and buttermilk to the mixture, alternating between them, and mix until just combined.
Gently fold in 2 1/2 cups of blueberries into the batter.
Spread the batter into the prepared pan and sprinkle the remaining 1/2 cup of blueberries and 1/4 cup of granulated sugar on top.
Bake the cake for 60 to 65 minutes until it's light golden and a toothpick inserted into the center comes out clean.
Let the cake cool completely in the pan, then use the parchment overhang to lift it out.
Dust with more granulated sugar if desired, slice, and serve. Enjoy!