01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a medium bowl, whisk together flour, baking powder, baking soda, salt, and poppy seeds.
03 - In a large bowl, cream together butter and sugar until light and fluffy, about 2 minutes.
04 - Beat in egg, lemon zest, lemon juice, and vanilla extract until fully combined.
05 - Gradually add dry ingredients to wet ingredients, mixing until just combined. Do not overmix.
06 - Scoop tablespoon-sized balls of dough onto prepared baking sheets, spacing 2 inches apart.
07 - Bake for 10 to 12 minutes until edges are lightly golden. Cool on baking sheet for 5 minutes, then transfer to wire rack.
08 - In a medium bowl, beat cream cheese and butter together until smooth.
09 - Add powdered sugar, lemon juice, vanilla, and salt. Beat until light and fluffy.
10 - Once completely cool, spread or pipe frosting onto each cookie. Garnish with extra lemon zest or poppy seeds if desired.