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 bowl, whisk together the flour, sugar, poppy seeds, baking powder, baking soda, and salt until well combined.
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. A few small lumps are acceptable.
05 - Divide the batter evenly among the prepared muffin cups, filling each about 3/4 full.
06 - Bake for 18–20 minutes, or until a toothpick inserted into the center of a muffin comes out clean or with just a few moist crumbs.
07 - Allow muffins to cool in the tin for 5 minutes, then carefully transfer to a wire rack to cool completely before serving.