Preheat oven to 350 degrees F. Have ready two large baking sheets lined with parchment paper.
Mix together the flour, baking soda, salt and cocoa powder and set aside.
In a large mixing bowl using an electric mixer, beat the butter and sugar until creamy. Add the egg and beat until mixed, then beat in the vanilla. Add the buttermilk and flour mixture alternately until you have a smooth, thick, batter.
Using a generously heaping tablespoon, drop the dough onto the baking sheets spacing 2 inches apart. Bake for 12-14 minutes or until cookies appear set and spring back when touched. Remove from baking sheets and let cool.
Set a decorating bag in a glass and pull sides down to make a little cuff . Do not snip the bottom or add a decorating tip at this point.
To make the white frosting, combine the powdered sugar, cream, milk and corn syrup in a bowl and stir until thick. Add corn syrup and vanilla. Add more milk, 1 teaspoon at a time, until batter is thin but not runny. Transfer to the decorating bag.
Repeat the same steps with the pink frosting recipe, only add the red food coloring Transfer to another decorating bag.
When cookies are completely cool, turn them over so that the flat side is up. Snip the tip off the white decorating bag and pipe filling over half of each cookie. Repeat with the pink icing.
Let cookies sit at room temperature until the icing sets.