Preheat your oven to 375°F (190°C). Line a muffin tray with paper liners or lightly grease each cup.
In a large bowl, whisk together the flour, sugar, baking powder, and salt.
In a separate bowl, mix the melted butter, egg, milk, and vanilla.
Pour the wet mixture into the dry ingredients and stir gently until just combined. Do not overmix.
Fold in the blueberries, making sure they are evenly distributed.
Fill each muffin cup about three quarters full.
Bake for 18 to 22 minutes or until the tops are golden and a toothpick inserted into the center comes out clean.
Let the muffins cool for a few minutes before serving.