Mix sugar with lemon zest - Add sugar and zest from 2 lemons to your stand mixer bowl and rub together to release the lemon oil.
Zest from 2 large lemons, 150 grams granulated sugar
Cream butter with sugar - Add softened butter and beat with the paddle attachment for at least 2 minutes until well incorporated and creamy.
113 grams unsalted butter
Incorporate sourdough starter - Add the egg yolk, vanilla extract, lemon juice, sourdough starter and continue beating for at least another 2 minutes until fluffy and creamy.
1 large egg yolk, 3 grams pure vanilla extract, 5 grams lemon juice, 50 grams sourdough starter discard
Add dry ingredients - Sift flour and baking soda directly into the wet ingredient mixture in the stand mixer bowl, sprinkle salt on top, stir until incorporated. Stop the mixer and scrape down the sides and bottom of the bowl as necessary. Chill in the fridge for 15 minutes before scooping and rolling if the dough seems too sticky to handle right away.
180 grams all-purpose flour, 3 grams baking soda, 2 grams kosher salt
Scoop and roll - Portion the cookie dough with a 1 ½-tablespoon cookie scoop and place them on a lined baking sheet. Roll into balls. Cover and refrigerate while the oven preheats. You don’t need a long chill for this dough.
Preheat the oven to 350°F.
Prepare the lemon sugar topping - Mix together granulated sugar and zest from 1 lemon in a shallow bowl.
50 grams granulated sugar, Zest from 1 large lemon
Bake - Roll the dough balls in lemon sugar, place 12 on a half sheet baking sheet, and bake for about 13 minutes, until the edges of the cookies start to turn lightly golden.
Cool - Remove the baking sheet from the oven, and allow the cookies to sit on the baking sheet to finish baking from the residual heat for 10-15 minutes before removing them to a wire rack to cool completely.