01 - Beat softened butter and powdered sugar in large bowl until light and fluffy, approximately 2-3 minutes.
02 - Blend in lemon juice, lemon zest, and vanilla extract until thoroughly incorporated.
03 - Add salt, flour, and cornstarch; mix until soft dough forms and no dry pockets remain.
04 - Divide dough in half, roll into 1-inch diameter logs, wrap in plastic, and refrigerate 30 minutes.
05 - Heat oven to 350°F and line baking sheets with parchment paper.
06 - Unwrap dough and cut into 1/4-inch rounds; arrange on prepared sheets 1 inch apart.
07 - Bake 10-12 minutes until edges are barely golden; do not overbake.
08 - Let cookies cool 5 minutes on sheets, then gently toss in powdered sugar while warm.
09 - Transfer to wire rack to cool completely; dust with additional powdered sugar before serving.