01 - Preheat oven to 375°F. Line a 12-cup muffin tin with paper liners or grease lightly with butter.
02 - In a large bowl, whisk together flour, sugar, poppy seeds, baking powder, baking soda, and salt until well combined.
03 - In a separate medium bowl, whisk eggs, milk, melted butter, lemon juice, lemon zest, and vanilla extract until smooth and blended.
04 - Pour wet ingredients into dry ingredients. Stir gently with a spatula until just combined—do not overmix. Small lumps in the batter are acceptable.
05 - Divide batter evenly among prepared muffin cups, filling each about three-quarters full.
06 - Bake for 18 to 20 minutes until a toothpick inserted into the center comes out clean.
07 - Let muffins cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.