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.
03 - Beat butter and sugar in a large bowl until light and fluffy, approximately 2 minutes.
04 - Add eggs one at a time, beating well after each addition. 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 ingredients. Mix until just combined.
06 - Divide batter evenly among cupcake liners, filling each about 2/3 full.
07 - Bake for 16 to 18 minutes, or until a toothpick inserted in the center comes out clean.
08 - Let cupcakes cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.
09 - Beat butter and cream cheese together 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 additional lemon zest or poppy seeds if desired.