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, and salt until well combined.
03 - In a large bowl, beat softened butter and granulated sugar with electric mixer on medium speed until light and fluffy, approximately 2-3 minutes.
04 - Beat in eggs one at a time, fully incorporating each before adding the next. Mix in lemon juice, lemon zest, and vanilla extract until combined.
05 - Gradually add dry ingredients to wet mixture, mixing on low speed until just incorporated. Do not overmix.
06 - Drop rounded tablespoons of dough onto prepared baking sheets, spacing cookies 2 inches apart to allow for spreading.
07 - Bake for 10-12 minutes until edges are lightly golden and centers appear set. Rotate pans halfway through baking for even results.
08 - Allow cookies to rest on baking sheets for 5 minutes, then transfer to wire racks to cool completely before frosting.
09 - In a medium bowl, whisk powdered sugar, 2 tablespoons lemon juice, lemon zest, and melted butter until smooth and spreadable. Add additional lemon juice 1 teaspoon at a time if thinner consistency is desired.
10 - Spread lemon frosting generously over cooled cookies. Allow frosting to set for 15 minutes before serving or storing.