Poppy seeds lend a pleasant crunch to these aromatic, lemony muffins.
Preheat oven to 350 degrees. Line a standard 12-cup muffin tin with baking cups. In a medium bowl, whisk together flour, baking powder, baking soda, and salt. In a separate bowl, whisk together sugar, eggs, zest, juice, and milk. Whisk in butter. Stir wet ingredients into dry ingredients, until just combined. Stir poppy seeds into batter.
Divide batter evenly between muffin cups, adding a scant 1/4 cup to each. Sprinkle with sugar and poppy seeds, if desired. Bake until tops spring back when lightly touched, about 20 minutes. Cool 5 minutes in pan, then transfer to wire rack to cool completely.