Preheat your oven to 350°F (175°C). Grease and flour a 9x13-inch baking pan or line it with parchment paper for easy removal.
In a large mixing bowl, whisk together the flour, sugar, baking powder, baking soda, and salt until well combined.
In another bowl, beat the softened butter until creamy. Add the buttermilk, eggs, and vanilla extract, mixing until smooth.
Gradually add the wet ingredients to the dry ingredients, stirring gently until just combined. Be careful not to overmix.
Fold in the blueberries and lemon zest, if using, until evenly distributed throughout the batter.
Pour the batter into the prepared baking pan and spread it evenly.
Bake in the preheated oven for 35-40 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for about 10 minutes, then transfer it to a wire rack to cool completely. Dust with powdered sugar before serving, if desired.