01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a medium bowl, whisk together the flour, baking soda, and salt. Set aside.
03 - In a large mixing bowl, beat the softened butter and granulated sugar with an electric mixer until pale, light, and fluffy, about 2 to 3 minutes.
04 - Add the egg and egg yolk, beating until fully incorporated. Mix in the lemon zest, lemon juice, and vanilla extract until well combined.
05 - Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed just until the flour is incorporated. Do not overmix.
06 - Scoop tablespoon-sized portions of dough and roll into even balls. If desired, roll each ball in granulated sugar to coat.
07 - Place the dough balls 2 inches apart on the prepared baking sheets to allow for spreading.
08 - Bake for 9 to 11 minutes, until the edges are set but the centers remain soft and slightly underbaked for a chewy texture.
09 - Allow the cookies to rest on the baking sheets for 5 minutes, then transfer to a wire cooling rack to cool completely.