These bright and fresh lemon lime shortbread cookies are flavored with citrus zest and are dipped in icing with citrus juice.
1/2 pound (2 sticks) unsalted butter at room temperature
3/4 cup granulated sugar
1 egg yolk
Juice and zest of 1 lemon plus more zest for decorating
Juice and zest of 1 lime plus more zest for decorating
1–1/2 cups all-purpose flour plus more for dusting
1/2 cup cornstarch
1/2 teaspoon salt
Using an electric mixer, beat the butter and sugar together on low until just combined, about 30 seconds, followed by the yolk, lemon zest and lime zest. Beat in the flour, cornstarch and salt on low until just combined. The dough should still be crumbly. Flatten the dough into a disk, wrap it in plastic wrap and chill in the refrigerator for at least 30 minutes until firm.
On a lightly floured work surface, roll out the dough until it is 1/4 inch thick. Use a cookie cutter to cut out shapes. Chill the unbaked cookies in the refrigerator for 1 hour.
Preheat the oven to 275 degrees F. Bake the cookies on an ungreased sheet pan for 30 minutes until they are just baked through, but the tops have not browned.
Let the cookies cool completely. To make the icing, whisk together the confectioners’ sugar, lemon juice and lime juice. If the icing seems too thin, add a little more sugar. Dip or drizzle to the cookies with icing and sprinkle with zest.