Combine the butter and 6 tablespoons powdered sugar in a large mixing bowl and cream with an electric mixer on medium speed until very light and fluffy; this will take a couple of minutes.

Add the vanilla and lemon zest and beat until combined.

Sift the flour, cornstarch, and salt over the butter mixture. Beat on low speed until a cohesive dough forms, stopping to scrape the sides and bottom of the bowl a few times. (The dough will be crumbly at first but it will eventually come together.)

Stir a few times with a rubber spatula to ensure all of the dry ingredients are incorporated, then cover the bowl and refrigerate for 1 or 2 hours.

After the dough has chilled, preheat the oven to 350. Spray 2 large baking sheets with cooking spray.

Shape the dough into 1-inch balls and arrange 2 inches apart on the baking sheets.

Use the bottom of a flat-bottomed glass (or just use your palm) to flatten dough balls to 1/4-inch thickness. (If the glass sticks you can spray it lightly with cooking spray.) Don’t get the cookies too thin or they’ll burn!

Bake 12 to 14 minutes, until the cookies look set all over. The cookies WILL NOT brown.

Let the cookies sit for 1 minute on the baking sheets, then use a thin metal spatula (I use a large offset spatula) to transfer the cookies to a wire rack. Don’t use your fingers or the cookies will crumble.

Sift the remaining powdered sugar over the tops of the cookies while they’re still warm. (You can do a second coat after the cookies cool if you want.) Serve.

Cool cookies to room temperature before storing them—they don’t have to be room temp to serve them though!

Uneaten cookies can be stored at room temperature in an airtight container, layered with wax paper, for about a week

The cookies can also be frozen, also in an airtight container, for up to 3 months.