In a medium bowl, sift together the all-purpose flour, cornstarch, salt, and baking powder.
Set the oven temperature to 325°F.
In a large bowl, beat the unsalted butter, granulated sugar, and powdered sugar until light and fluffy, about 3 minutes.
Add the lemon zest, lemon juice, egg yolk, and lemon extract; beat until combined.
Slowly introduce the dry ingredients into the wet mixture in three stages, mixing on low speed until combined.
Remember to scrape down the bowl as necessary.
Shape the dough into a ball, cover it, and refrigerate for at least 1 hour to firm up.
Using a scoop, place 1-inch dough balls on parchment-lined baking sheets, ensuring they are spaced approximately 2 inches apart.
Gently press down each ball with the bottom of a glass.
Bake the cookies for 12-14 minutes until the edges are lightly golden.
Immediately after removing them from the oven, toss the hot cookies in the measured powdered sugar to coat.
Transfer them to a cooling rack. Once completely cooled, you may dust them lightly with powdered sugar again if desired.
