Preheat your oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners or lightly grease it.
In a large bowl, whisk together the flour, sugar, baking powder, baking soda, and salt.
In a separate bowl, whisk the melted butter, eggs, buttermilk, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and gently mix until just combined, do not overmix.
Toss the blueberries with 1 tablespoon of flour, then fold them gently into the batter.
Divide the batter evenly among the muffin cups, filling each about ¾ full. Sprinkle the tops with coarse sugar.
Bake for 22–25 minutes, or until the muffins are golden brown and a toothpick inserted in the center comes out clean.
Let the muffins cool in the pan for 5 minutes, then transfer to a wire rack to cool slightly before serving.