01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a medium bowl, whisk together the all-purpose flour, baking soda, and salt until evenly distributed. Set aside.
03 - In a large mixing bowl, beat the softened butter and granulated sugar with an electric mixer on medium speed until pale, light, and fluffy, approximately 2 to 3 minutes.
04 - Add the whole egg and beat until fully absorbed. Mix in the egg yolk, followed by the lemon zest, fresh lemon juice, and vanilla extract, blending until the mixture is smooth and homogeneous.
05 - Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed just until the flour is incorporated. Avoid overmixing to keep the cookies tender.
06 - Scoop tablespoon-sized portions of dough and roll into even balls. If desired, roll each ball in granulated sugar to coat before arranging on the prepared baking sheets, spacing them 2 inches apart.
07 - Bake for 9 to 11 minutes, or until the edges are lightly set while the centers remain soft and appear slightly underbaked.
08 - Allow the cookies to rest on the baking sheets for 5 minutes to firm up, then transfer to a wire cooling rack to cool completely.