Black and White Cookies

INGREDIENTS
1 cup unsalted butter
1 3/4 cups white sugar
4 eggs
1 cup milk
1/2 teaspoon vanilla extract
1/4 teaspoon lemon extract
2 1/2 cups cake flour
2 1/2 cups all-purpose flour
1 teaspoon baking powder
1/2 teaspoon salt

4 cups confectioners' sugar
1/3 cup boiling water
1 (1 ounce) square bittersweet chocolate, chopped
DIRECTIONS
Preheat oven to 375 degrees F (190 degrees C). Butter 2 baking sheets.
In a medium bowl, cream together butter and sugar until smooth. Beat in eggs one at a time, then stir in the milk, vanilla, and lemon extract. Combine cake flour and all-purpose flour, baking powder, and salt; gradually blend into the creamed mixture. Drop tablespoonfuls of the dough 2 inches apart on prepared baking sheets.
Bake until edges begin to brown, about 20 to 30 minutes. Cool completely.
Place confectioners sugar in large bowl. Mix in boiling water one tablespoon at a time until mixture is thick and spreadable. (Add more than the indicated amount if you need to).
Transfer half of the frosting to the top of a double boiler set over simmering water. Stir in the chocolate. Warm mixture, stirring frequently, until the chocolate melts. Remove from heat.
With a brush, coat half the cookie with chocolate frosting and the other half with the white frosting. Set on waxed paper until frosting hardens.