Garnish with topping of your choice: strawberries, chocolate shavings, chopped smoked pecans, etc.
Instructions
Combine Coca-Cola and buttermilk; set aside.
Beat butter at low speed with an electric mixer until creamy. Gradually add sugar; beat until blended. Add egg and vanilla; beat at low speed until blended.
Combine flour, cocoa, and baking soda. Add to butter mixture alternately with cola mixture; begin and end with flour mixture. Beat at low speed just until blended.
Stir in marshmallows. Pour batter into a greased and floured 13×9-inch pan. Bake at 350° for 30 to 35 minutes. Remove from oven; cool 10 minutes.
Top with white frosting and other toppings of your choice such as chocolate shavings, strawberries, or chopped smoked pecans.