01 - Preheat the 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, approximately 2 minutes.
04 - Add eggs one at a time, mixing thoroughly after each addition. Blend in lemon juice, lemon zest, and vanilla extract.
05 - Add dry ingredients to wet mixture in three additions, alternating with milk, starting and ending with dry ingredients. Mix until just combined—avoid overmixing.
06 - Distribute batter evenly among cupcake liners, filling each approximately two-thirds full.
07 - Bake for 16 to 18 minutes, until a toothpick inserted in the center emerges clean.
08 - Let cupcakes rest in the pan for 5 minutes, then transfer to a wire rack to cool fully.
09 - Beat butter and cream cheese until smooth. Gradually incorporate powdered sugar while beating well. Blend in lemon juice, lemon zest, and salt.
10 - Generously frost cooled cupcakes with lemon cream cheese frosting. Decorate with additional lemon zest or poppy seeds if desired.