Preheat the oven to 375°F (190°C) and line a 12-cup muffin pan with paper liners.In one bowl, whisk together the flour, baking powder, baking soda, and salt.In another bowl, whisk the melted butter, sugar, eggs, vanilla, sour cream, and milk until smooth.Gradually fold the dry ingredients into the wet ingredients until just combined.Toss the blueberries with 1 tablespoon of flour, then gently fold them into the batter.Divide the batter evenly among the muffin cups, filling each about ¾ full.Sprinkle the tops with coarse sugar if desired.Bake for 20–22 minutes, or until the tops are golden and a toothpick inserted in the center comes out clean.Cool in the pan for 5 minutes before transferring the muffins to a wire rack to cool completely.
