Preheat the oven to 350 degrees F. Spray 9x13" baking dish with cooking spray and set aside.
In a large bowl with electric mixer, beat the butter, sugar, and lemon zest until well combined, about 2-3 minutes.
Add the eggs, one at a time, scraping down the sides between each addition, followed by the vanilla extract.
In a separate bowl, whisk together the flour, baking powder, and salt.
Add half of the flour mixture to the mixer bowl and beat until just combined. Add half of the buttermilk and beat until just combined. Repeat with remaining flour and buttermilk.
Fold in the blueberries.
Pour batter into prepared baking dish.
Sprinkle with remaining 2 tablespoon granulated sugar.
Bake in the preheated oven for 40-45 minutes, until golden brown and baked through.
Let cool 10 minutes, then cut into squares and enjoy!