Whisk together the flour, cornstarch, baking soda, and salt in a medium bowl. Set aside.
2½ cups all-purpose flour, 1 & 1/2 tbsp cornstarch, ¾ tsp baking soda, ¼ tsp salt
In the bowl of a stand mixer rub the sugar with the lemon zest using your fingers to release the oils.
2 tbsp lemon zest, 1 cup granulated sugar
In the same bowl of a stand mixer fitted with the paddle attachment, cream the Plugrà butter, lemon granulated sugar mixture, and brown sugar on medium-high for 3 to 4 minutes until light and fluffy.
1 cup Plugrà unsalted butter, 2 tbsp light brown sugar
Add the egg and egg yolk one at a time, mixing well after each addition. Add the lemon juice, lemon zest, lemon extract, and vanilla extract. Mix until combined. Slight curdling is normal.
1 large egg, 1 large egg yolk, 1½ tbsp fresh lemon juice, ½ tsp lemon extract, 1 tsp vanilla extract
Add the dry ingredients and mix on low just until the flour disappears. Do not overmix.
Cover the dough and refrigerate for at least 2 hours or up to overnight. (See notes below for two chilling methods, pick whichever works best for you!)
Preheat the oven to 325°F and line two baking sheets with parchment paper.
Scoop 1.5 tablespoon dough balls, roll smooth between your palms, then roll in the plain granulated sugar. Place 2 inches apart on the prepared baking sheets.
⅓ cup granulated sugar
Bake for 10 to 11 minutes, until the edges are just set and the centers look slightly underdone.
If any cookies spread more than you'd like, place a round cookie cutter, the rim of a mug, or a small bowl over each cookie right out of the oven (while still hot and pliable) and gently swirl it in a circle. This pushes the edges back in and gives you perfectly round, tighter cookies.
Cool on the pan for 10 minutes, then transfer to a wire rack to cool completely before filling.