01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl.
03 - Beat butter and sugar in a large bowl until light and fluffy, about 2-3 minutes.
04 - Beat in eggs one at a time, then add lemon juice, lemon zest, and vanilla extract, mixing until combined.
05 - Gradually add the dry ingredients, mixing until just incorporated.
06 - Drop rounded tablespoons of dough onto prepared baking sheets, spacing 2 inches apart.
07 - Bake for 10-12 minutes, or until edges are lightly golden.
08 - Allow cookies to cool on the baking sheets for 5 minutes, then transfer to wire racks to cool completely.
09 - Whisk powdered sugar, lemon juice, lemon zest, and melted butter until smooth and spreadable.
10 - Frost tops of cooled cookies with lemon frosting. Let set for 15 minutes before serving.