Instructions

1. Preheat oven to 350F. Line 2 large baking sheets with parchment paper.
2. In a medium bowl, whisk together the flour, cornstarch, and salt. Set aside.
3. Using an electric mixer, beat together the butter and 1/2 cup of the confectioners sugar with an electric mixer until pale and fluffy. Beat in the lemon zest and vanilla. At a low speed, mix in the flour mixture just until a soft dough forms. (It will seem crumbly at first, but will then come together.) Freeze the dough for 15 minutes.
4. Put the remaining 1/2 cup of powdered sugar in a bowl. Roll a teaspoon of dough into a ball and drop into the sugar, turning to coat. Reshape if necessary, then transfer to a baking sheet. Repeat, spacing balls 3/4 inch apart, until the baking sheets are filled.
5. Bake the cookies until tops are slightly cracked but still pale (bottoms will be pale golden), 12-15 minutes, rotating pans halfway. Transfer cookies to a rack to cool completely.