01 - Preheat oven to 350°F. Line a 12-cup muffin pan with paper liners.
02 - Whisk together flour, poppy seeds, baking powder, baking soda, and salt in a medium bowl. Set aside.
03 - Beat butter and sugar in a large bowl until light and fluffy, about 2 minutes.
04 - Add eggs one at a time, beating well after each. Mix in lemon juice, lemon zest, and vanilla extract.
05 - Add dry ingredients to wet mixture in three additions, alternating with milk, beginning and ending with dry. Mix until just combined.
06 - Divide batter evenly among liners, filling each about 2/3 full.
07 - Bake for 16-18 minutes, or until a toothpick inserted in center comes out clean.
08 - Cool in pan for 5 minutes, then transfer to wire rack to cool completely before frosting.
09 - Beat butter and cream cheese until smooth. Gradually add powdered sugar, beating well. Mix in lemon juice, lemon zest, and salt.
10 - Frost cooled cupcakes generously with lemon cream cheese frosting. Garnish with extra lemon zest or poppy seeds if desired.