Preheat the oven to 400F. Line a 12-cup muffin tin with liners or cooking spray.
Whisk together flour, sugars, baking powder, baking soda, and salt in a medium bowl until evenly mixed.
In a large bowl, whisk together buttermilk, oil, eggs, and vanilla until smooth. Fold in the dry ingredients from step 2 using a rubber spatula then mix until well combined. Finally, mix in the blueberries.
Fill each muffin cup about 2/3rds full with batter then sprinkle tops with coarse sugar. Bake in the oven for 22-26 minutes or until the tops are golden and a toothpick inserted in the center of one muffin comes out clean. Repeat with remaining batter for the last 6 muffins.