Preheat the oven to 350 degrees F (175 degrees C) and grease and flour a 9x13 baking pan.
In a large bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
In a separate bowl, cream together the softened butter and sugar with an electric or hand mixer until light and fluffy.
Beat in the eggs one at a time, mixing well after each addition.
Add in the lemon zest and vanilla extract and mix until combined.
Alternate between adding the dry ingredients and the milk to the wet ingredients, beginning and ending with the dry ingredients. Blend just until combined - don't overmix.
Gently fold in the fresh blueberries.
Spread the batter evenly into the prepared baking pan.
Bake the cake in the preheated oven for 35-40 minutes, or until a toothpick inserted into the center comes out clean.
Let the cake cool completely in the pan before frosting, if desired. This cake is delicious with a simple powdered sugar glaze, cream cheese frosting, or a scoop of vanilla ice cream.
Notes
Use fresh blueberries for the best flavor and texture in your cake. Frozen will work but may release too much juice.
Room temperature ingredients mix together more easily, so let the butter, eggs, and milk sit out for a while before starting.
Don't overmix the cake batter. Overmixing will make the cake tough.