-
1
Make cookies:
-
2
Preheat oven to 350F.
-
3
Whisk together flour, baking soda, and salt in a bowl.
-
4
Stir together buttermilk and vanilla in a cup.
-
5
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.
-
6
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.
-
7
Mix until smooth.
-
8
Spoon 1/4 cups of batter about 2 inches apart onto a buttered large baking sheet.
-
9
Bake in middle of oven until tops are puffed and pale golden, and cookies spring back when touched, 15 to 17 minutes.
-
10
Transfer with a metal spatula to a rack and chill (to cool quickly), about 5 minutes.
-
11
Make icings while cookies chill:
-
12
Stir together confectioners sugar, corn syrup, lemon juice, vanilla, and 1 tablespoon water in a small bowl until smooth.
-
13
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.
-
14
Ice cookies:
-
15
Turn cookies flat sides up, then spread white icing over half of each and chocolate over other half.
