Preheat your oven to 375°F (190°C) and line a muffin tin with paper liners.
In a large bowl, mix together the flour, sugar, baking powder, baking soda, and salt.
In another bowl, whisk together the melted butter, egg, milk, and vanilla extract until combined.
Pour the wet ingredients into the dry ingredients and mix until just combined.
Gently fold in the fresh blueberries, being careful not to overmix.
Divide the batter evenly among the prepared muffin cups.
Bake in the preheated oven for 20 minutes or until a toothpick comes out clean.
Let the muffins cool in the pan for 5 minutes before transferring them to a wire rack.
Enjoy warm or at room temperature.
Store any leftovers in an airtight container.