01 - Preheat oven to 350°F. Line two baking sheets with parchment paper and set aside.
02 - In a medium bowl, whisk together the 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, about 2 to 3 minutes.
04 - Beat in the whole egg followed by the egg yolk, then mix in the lemon zest, fresh lemon juice, and vanilla extract until thoroughly combined.
05 - Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed just until the dough comes together. Be careful not to overmix.
06 - Scoop tablespoon-sized portions of dough and roll into even balls. If desired, roll each ball in granulated sugar for a sparkling coating.
07 - Place the dough balls 2 inches apart on the prepared baking sheets to allow for spreading.
08 - Bake for 9 to 11 minutes, or until the edges are lightly set but the centers still appear soft and slightly underbaked.
09 - Allow the cookies to rest on the baking sheets for 5 minutes, then transfer to a wire cooling rack to cool completely.