Preheat the oven to 350F (180C) and line cookie sheets with baking paper or silicone baking mats.
In a medium bowl, whisk together the flour, cornstarch, baking soda and salt. Set aside.
In a small bowl, pinch together the 1 1/3 cup sugar and lemon zest. Essentially, you want to rub the lemon zest into the sugar - you only need to do this for about 30 seconds.
In a large bowl, beat together the butter with the sugar and lemon zest mixture.
Beat in the egg, additional egg yolk, vanilla extract and lemon extract.
Mix the dry ingredients into the butter mixture, starting with the mixer on a low speed and gradually increasing to medium speed until combined.
Pour the 1/3 cup granulated sugar onto a small plate. Spoon the dough into balls with about 1 to 1.5 tablespoons of dough each and roll each dough ball in the sugar.
Place the cookie dough balls about 2 inches apart on the lined cookie sheets.
Bake 1 sheet at a time in the middle of the oven for about 9-11 minutes, or until the tops look set. Cool on the cookie tray for at least 10 minutes before transferring to a wire rack to continue cooling.