No time to bake? Buy Dutch-cocoa cookies and all you need to make is the fluffy filling for this dessert.
Heat oven to 350°F. Grease 2 large baking sheets. In medium bowl, combine flour, cocoa, and baking soda. In large bowl, with mixer on high speed, beat together butter and sugar until light and fluffy, about 3 minutes. Add egg and vanilla, and beat to combine. Alternate adding flour mixture and buttermilk in small batches, beginning and ending with flour mixture. Mix until smooth, occasionally scraping sides of bowl.
With a tablespoon, spoon mounds of batter 2 inches apart onto baking sheets. Sprinkle half with crystal sugar. Bake 15 minutes or until tops are puffed and cakes spring back when touched. Transfer to a rack and cool completely.
In medium bowl, with mixer on high speed, beat together butter, powdered sugar, marshmallow cream, and vanilla until smooth, about 3 minutes. Add a drop or two of food coloring, and mix to tint pink. Makes about 1-1/2 cups of filling.
Spread a rounded tablespoon of filling on flat sides of half the cakes. Top with other cakes.