Preheat oven to 375°F (190°C) and line a muffin pan with paper liners.
Toss blueberries with 1 tablespoon of the flour and set aside.
In a large bowl, whisk together flour, sugar, baking powder, and salt.
In a second bowl, whisk together butter, egg, buttermilk, and vanilla until combined.
Pour wet mixture into dry and fold gently until just combined.
Fold in the flour-coated blueberries gently—do not overmix.
Fill muffin cups ⅔ full and bake for 22–25 minutes until golden and toothpick comes out clean.
Let muffins cool in the pan for 5 minutes, then transfer to a wire rack.