01 - Preheat oven to 375°F. Line a 12-cup muffin tin with paper liners or grease lightly.
02 - In a large bowl, whisk together flour, sugar, baking powder, baking soda, and salt until well blended.
03 - In a separate bowl, whisk eggs, milk or buttermilk, melted butter, lemon zest, lemon juice, and vanilla extract until smooth.
04 - Pour wet mixture into dry ingredients and fold gently with a spatula until just combined; avoid overmixing.
05 - Fold in blueberries carefully to distribute evenly without breaking fruit.
06 - Divide batter evenly among muffin cups, filling each approximately three-quarters full. Sprinkle tops with coarse sugar if using.
07 - Bake for 20 to 22 minutes until golden on top and a toothpick inserted comes out clean.
08 - Allow muffins to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.