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 blended.
03 - In a large bowl, beat softened butter and granulated sugar with an electric mixer until light and fluffy, about 2–3 minutes.
04 - Beat in eggs one at a time, ensuring each is fully incorporated before adding the next. Mix in lemon juice, lemon zest, and vanilla extract until combined.
05 - Gradually add dry ingredients to the wet mixture, mixing on low speed until just incorporated. Do not overmix.
06 - Drop rounded tablespoons of dough onto prepared baking sheets, spacing about 2 inches apart to allow for spreading.
07 - Bake for 10–12 minutes or until edges are lightly golden and centers are set.
08 - Let cookies cool on baking sheets for 5 minutes, then transfer to wire racks to cool completely before frosting.
09 - Whisk powdered sugar, lemon juice, lemon zest, and melted butter (if using) until smooth and spreadable. Adjust consistency with additional lemon juice if needed.
10 - Once cookies are completely cool, spread or drizzle lemon frosting over the tops. Allow frosting to set for about 15 minutes before serving.