01 - Preheat oven to 375°F. Line a 12-cup muffin tin with paper liners or grease lightly.
02 - Whisk together flour, sugar, poppy seeds, baking powder, baking soda, and salt in a large bowl.
03 - In a separate bowl, whisk together milk, melted butter, eggs, sour cream, lemon zest, and vanilla extract until homogeneous.
04 - Gently fold the wet ingredients into the dry until just combined without overmixing.
05 - Spoon batter evenly into the prepared tin, filling each cup 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.