Wash and dry your lemon. Use a fine grater or zester to remove the yellow outer layer (the zest). Avoid the white part under the skin because it tastes bitter.
Then cut the lemon and squeeze out the juice. You need about 2 tablespoons.
Preheat your oven to 180°C / 350°F, so it is hot and ready when your dough is chilled and shaped.
Add the softened butter and granulated sugar to a medium mixing bowl.
Use a hand mixer or stand mixer to beat them together on medium speed. Mix for 2–3 minutes until the butter looks pale and fluffy.
If you are mixing by hand, use a sturdy whisk or wooden spoon and take a bit more time.
Crack the egg into the bowl with the butter and sugar. Add the lemon zest and lemon juice.
Beat again on low to medium speed until everything looks combined.
In a separate bowl, whisk together All-purpose flour, Cornstarch, Baking soda, Salt. Stir with a spoon or whisk until everything is evenly combined.
Pour the dry mixture into the bowl with the wet ingredients.
Use a spatula or mixer on low speed to gently fold everything together. Stop mixing as soon as you no longer see dry flour.
The dough will be soft and slightly sticky, but it should hold together.
Cover the bowl with plastic wrap or a plate and place it in the fridge for 20–30 minutes. If your kitchen is very warm, you can chill the dough a bit longer, up to 45 minutes.
Pour the powdered sugar into a small shallow bowl. Take the chilled dough out of the fridge. Use a small cookie scoop or a spoon to scoop out portions of dough, about 1 to 1.5 tablespoons each. Roll each piece into a ball with your hands.
Drop each ball into the powdered sugar and roll it until it is lightly coated all around. Place the coated dough balls onto the prepared baking tray, leaving space between them so they can spread a bit while baking.
Place the tray in the preheated oven and bake for 10–12 minutes.
Take the tray out of the oven and let the cookies rest on the tray for about 5 minutes.
