Add the flour, cornstarch, baking powder, and baking soda, and mix just until the dough comes together. Avoid overmixing so the cookies stay soft and chewy.
Cover the bowl with plastic wrap and chill the dough in the fridge for at least 1 hour. You can also chill it overnight for even easier scooping.
Use a large cookie scoop (or measure about 3 tablespoons of dough) and roll each portion into a smooth ball. Roll each dough ball first in granulated sugar, then in powdered sugar to coat.
Place the coated dough balls on a parchment-lined baking sheet and bake in a preheated 180°C (350°F) oven for about 10 minutes.
The cookies should stay light in color; don’t overbake them if you want a soft, chewy center.
Let the cookies cool on the baking sheet for 5 minutes, then transfer them to a wire rack to cool completely.
Notes
Do not overbake these cookies! These cookies should stay light in color. Take them out at around 10 minutes to keep the centers soft and chewy.
Space them apart. The cookies spread as they bake, so leave enough room on the baking sheet to keep them from touching.
Measure your flour correctly! Too much flour can make the cookies dry. Spoon the flour into your measuring cup and level it off instead of packing it in.
Chill the dough. Even a short chill helps the cookies hold their shape, crack nicely on top, and stay thick and chewy.
Zest your lemons carefully. When zesting the lemons, avoid the bitter white pith beneath the skin. Use a microplane or fine grater to get the most aromatic zest possible.
Double coat in sugar. Rolling the dough in granulated sugar first helps the powdered sugar stick better and gives the cookies a crisp outside.
Use fresh lemons. Fresh lemon juice and zest give the cookies the strongest, brightest citrus flavor. Bottled lemon juice won’t taste the same.
Room-temperature eggs. They mix more smoothly into the batter and help the cookies bake evenly.
Use a cookie scoop. For evenly sized cookies that bake uniformly, use a small or medium cookie scoop.
Don’t overmix the dough. Overmixing develops gluten and can make the cookies tough. Stop mixing as soon as the flour disappears.
Cool on the sheet first. Letting the cookies rest for a few minutes on the baking sheet helps them set without drying out, keeping that perfect soft texture.