Preheat your oven to 375°F (190°C). Line a muffin tin with paper liners or grease it lightly with cooking spray.
In a large mixing bowl, whisk together the flour, granulated sugar, baking powder, baking soda, and salt until well combined.
In another bowl, mix the melted butter, egg, vanilla extract, and buttermilk until smooth.
Pour the wet ingredients into the dry ingredients and gently fold until just combined. Be careful not to overmix; a few lumps are okay.
Gently fold in the blueberries, ensuring they are evenly distributed throughout the batter.
Divide the batter evenly among the muffin cups, filling each about 3/4 full.
Sprinkle the coarse sugar on top of each muffin for added sweetness and crunch.
Bake in the preheated oven for 18-22 minutes or until a toothpick inserted into the center comes out clean.
Allow the muffins to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.