Get the oven preheating to 350 degrees F. Line a baking sheet with parchment paper.
In a medium bowl, stir together the softened butter, sugar, and lemon zest until combined.
Mix in the egg yolk, lemon juice, and lemon extract until well combined.
Stir in flour, cornstarch, baking soda, and salt until well combined.
Chill the dough in the fridge for about 15 minutes while the oven finishes preheating.
Roll the dough into two balls and roll the balls in extra white granulated sugar, then place on the lined baking sheet.
Bake for 11–14 minutes until the edges are firm and set and the centers are just set.
Allow the cookies to cool on the baking sheet for about 10 minutes.
