01 - Preheat the 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 the flour, sugar, poppy seeds, baking powder, baking soda, and salt until well blended.
03 - In a separate 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 three-quarters full.
06 - Bake for 18 to 20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
07 - Allow the muffins to cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.