This is just one of many recipes for Black and White Cookies. They're quite popular in New York City, and they've been well represented in many TV shows that take place in New York City (like Seinfeld) by having Black and White Cookies the topic of many episodes. The cookie features a soft base that's a cross between sponge cake and shortbread, then half of the cookie is frosted with a white icing and the other half is frosted with a dark chocolate icing. It's easier to frost them all with the white icing first, then make the chocolate icing and frost them 'black' while it's still spreadable.
Preheat oven to 375°F. Spray 2 baking sheets with nonstick spray, or line with parchment paper, and set aside.
In large mixing bowl, combine sugar and butter. Mix by hand or with electric mixer. Add eggs, milk and vanilla and lemon extracts, and mix until smooth.
In medium bowl, combine cake flour, all-purpose flour, baking powder and salt. Stir until mixed. In batches, add dry mixture to the wet, stirring well after each addition.
Using a soup spoon, place heaping spoonfuls of the dough 2 inches apart on the baking sheets. Bake until edges begin to brown, 18 to 20 minutes. Cool completely.
Place confectioners' sugar in large mixing bowl. Gradually stir in enough boiling water to the sugar to make a thick, spreadable mixture.
Put half the frosting in the top half of a double-boiler. Add the chocolate and corn syrup, and set over simmering water. Warm the mixture, stirring, until chocolate is melted and frosting is smooth. Turn off the heat, but leave chocolate frosting over hot water to keep it spreadable.
With a brush, coat half of the top of each cookie with chocolate frosting, and the other half with white frosting. Set cookies aside to allow frosting to dry, then store cookies in an airtight container.