Preheat oven to 350°F.
Sift the flour before measuring. In a medium bowl, add the sifted flour, baking powder, salt, sugar and lemon zest. (Keep the zested lemons for another purpose, stored in the refrigerator.)
In a small bowl, combine the melted butter with the milk and the eggs, using a whisk to mix until blended.
Pour the milk mixture over the dry ingredients. Using a spatula, fold the ingredients together being very gentle and taking care not to over-mix the batter.
Prepare the muffin pan by spraying each cup with cooking spray (or brush with a light coating of melted butter, or use paper cupcake liners).
Fill each cup with batter leaving about 1/2 inch of room from the top. Using a small spatula or knife, add about 1/4 cup of the blueberries by gently folding and pushing them into the batter. It is very important not to over work the batter — be gentle.
Sprinkle each muffin with about 1/2 teaspoon or so of sugar.
Bake for about 20 to 25 minute, until a toothpick inserted in the center comes out clean and the muffins are slightly golden on top.
