This is a classic New York treat, found in just about every bakery in the city. The cookie is flavored with lemon and vanilla, and the cookies are glazed with half-white and half-chocolate icing, which dries to a slightly hard finish. If you do not have cake flour, you can use 7/8 cup all-purpose flour plus 2 tbsp cornstarch for each cup of cake flour. This recipe is adapted from the America's Test Kitchen Family Baking Book by Caroline Russock at Serious Eats. http://bit.ly/6aToYv