Preheat the oven to 375°F (190°C). Line a 12-cup muffin pan with paper liners.
In a medium bowl, whisk together the flour, baking powder, and salt.
In a separate large bowl, whisk together the melted butter and sugar.
Add the eggs, milk, vanilla extract, and optional lemon zest. Whisk until combined.
Gradually add the dry ingredients to the wet ingredients. Stir gently until just combined. Do not overmix.
Gently fold the blueberries into the batter.
Divide the batter evenly among the muffin cups, filling each about three-quarters full.
Bake for 18–22 minutes, or until the tops are lightly golden and a toothpick inserted into the center comes out clean or with a few moist crumbs.
Let the muffins cool in the pan for 5 minutes.
Transfer to a wire rack and serve warm or allow them to cool completely.