01 - Preheat 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 flour, granulated sugar, poppy seeds, baking powder, baking soda, and salt until well blended.
03 - In a separate bowl, whisk eggs, milk, melted butter, lemon juice, lemon zest, and vanilla extract until smooth and fully incorporated.
04 - Pour wet ingredients into dry ingredients. Fold gently with a spatula until just combined—stop when flour streaks disappear. Do not overmix; small lumps are acceptable.
05 - Divide batter evenly among prepared muffin cups, filling each approximately three-quarters full.
06 - Bake for 18 to 20 minutes until golden brown and a toothpick inserted into the center comes out clean.
07 - Let muffins rest in tin for 5 minutes, then transfer to a wire rack to cool completely before serving.