01 - Preheat the oven to 375°F. Line a 12-cup muffin tin with paper liners or grease lightly with butter or cooking spray.
02 - In a large mixing bowl, whisk together the flour, sugar, poppy seeds, baking powder, baking soda, and salt until well blended.
03 - In a separate medium bowl, whisk the eggs, milk, melted butter, lemon juice, lemon zest, and vanilla extract until smooth and fully incorporated.
04 - Pour the wet ingredients into the dry ingredients. Stir gently with a spatula or wooden spoon until just combined—do not overmix. Small lumps in the batter are acceptable and ensure tender muffins.
05 - Divide the batter evenly among the prepared muffin cups, filling each about three-quarters full. Use a measuring cup or ice cream scoop for uniform portions.
06 - Bake for 18 to 20 minutes, or until a toothpick inserted into the center of a muffin comes out clean or with just a few moist crumbs.
07 - Let the muffins cool in the tin for 5 minutes before transferring to a wire rack to cool completely. Serve warm or at room temperature.