In the bowl of a stand mixer fitted with the paddle attachment, beat butter at medium speed until smooth, about 1 minute. Add confectioners’ sugar, lemon zest, and salt, and beat until smooth, about 1 minute. Add egg yolk, and beat until combined, about 1 minute. Add flour in two additions, beating just until combined after each addition. Turn out dough onto a lightly floured surface, and gently knead 3 to 4 times. Shape dough into a disk and wrap in plastic wrap. Refrigerate for 1 hour.