01 - In a large bowl, beat the softened butter and powdered sugar with an electric mixer until the mixture is light and fluffy, approximately 2-3 minutes.
02 - Add the fresh lemon juice, lemon zest, and vanilla extract to the butter mixture. Mix until fully incorporated and fragrant.
03 - Gradually add the salt, all-purpose flour, and cornstarch to the wet mixture. Mix on low speed until a soft, pliable dough forms, taking care not to overmix.
04 - Divide the dough into two equal portions. Roll each portion into a log approximately 1 inch in diameter. Wrap tightly in plastic wrap and refrigerate for at least 30 minutes until firm.
05 - Preheat the oven to 350°F. Line two baking sheets with parchment paper and set aside.
06 - Remove the chilled dough logs from the refrigerator and unwrap. Using a sharp knife, slice into rounds approximately 1/4 inch thick. Arrange on prepared baking sheets, leaving 1 inch of space between each cookie.
07 - Bake for 10-12 minutes, or until the edges are just beginning to turn a pale golden color. The centers should remain soft and pale.
08 - Remove from the oven and allow cookies to rest on the baking sheets for 5 minutes. While still warm, gently toss each cookie in powdered sugar until evenly coated.
09 - Transfer the coated cookies to a wire cooling rack and let cool completely. For an elegant presentation, give them a second light dusting of powdered sugar just before serving.