Preheat oven to 400°F. Grease a 12-cup muffin tin or line with paper liners.
In a large bowl, whisk together the flour, baking powder, baking soda and salt.
In a separate bowl, whisk together the melted butter, sugar, egg, buttermilk and vanilla.
Fold the wet ingredients into the dry ingredients just until combined, being careful not to overmix. Gently fold in the blueberries.
Scoop the batter into the prepared muffin cups, filling them about ¾ full.
Bake for 18-20 minutes, until a toothpick inserted in the center comes out clean.
Allow the muffins to cool in the tin for 5 minutes before transferring to a wire rack.
