Preheat oven to 350
- 1 1/4 cups all-purpose flour
- 1/2 teaspoon baking soda
- 1/2 teaspoon salt
- 1/3 cup well-shaken buttermilk
- 1/2 teaspoon vanilla
- 1/3 cup (5 1/3 tablespoons) unsalted butter, softened
- 1/2 cup granulated sugar
- 1 large egg
- 1 1/2 cups confectioners sugar
- 1 tablespoon light corn syrup
- 2 teaspoons fresh lemon juice
- 1/4 teaspoon vanilla
- 1 to 2 tablespoons water
- 1/4 cup unsweetened unsweetened cocoa powder
- I added some Black food coloring as well
- Whisk together flour, baking soda, and salt in a bowl. Stir together buttermilk and vanilla in a cup.
- Beat together butter and sugar in a large bowl with an electric mixer until pale and fluffy, about 3 minutes, then add egg, beating until combined well.
- Mix in flour mixture and buttermilk mixture alternately in batches at low speed (scraping down side of bowl occasionally), beginning and ending with flour mixture. Mix until smooth.
- Spoon 1/4 cups of batter about 2 inches apart onto a buttered large baking sheet. Bake in middle of oven until tops are puffed and pale golden, and cookies spring back when touched, 15 to 17 minutes.
- Transfer with a metal spatula to a rack and chill in refrigerator or freezer (to cool quickly), about 5 minutes.
- Stir together confectioners sugar, corn syrup, lemon juice, vanilla, and 1 tablespoon water in a small bowl until smooth.
- Transfer half of icing to another bowl and stir in cocoa, adding more water, 1/2 teaspoon at a time, to thin to same consistency as white icing.
Turn cookies flat sides up, then spread white icing over half of each and chocolate over other half.