Preheat oven to 350°F (175°C) and line a baking tray with parchment paper.
Whisk together flour, baking soda, salt, and cornstarch in a bowl.
Cream butter, granulated sugar, and brown sugar until light and fluffy.
Add egg, lemon juice, lemon zest, and vanilla extract and mix well.
Gradually combine dry ingredients with wet mixture until a soft dough forms.
Chill dough for 20–30 minutes for thicker cookies (optional but recommended).
Scoop dough into balls and roll in powdered sugar.
Place on prepared tray and bake for 10–12 minutes until edges are set.
Cool on tray for 5 minutes before transferring to a wire rack.
