Preheat your waffle iron.
To a large bowl, add the flour, sugar, baking powder, and salt. Whisk.
To a medium bowl, add the milk, eggs, oil, and vanilla. Whisk.
Pour the wet ingredients into the dry ingredients and mix until JUST combined. Do not overmix. There should be lots of lumps.
Gently fold in the blueberries.
Spray the waffle iron generously with oil. Scoop batter into the center (do not overfill), and cook until golden brown and crisp. Transfer to a wire rack to cool. Repeat with the remaining batter.