Created by LilyInTheValley on June 22, 2013
Step 1: Preheat oven to 350 degrees F. Grease 13x9x2-inch baking pan.
Step 2: In large bowl, stir together flour and granulated sugar. Set aside.
Step 3: TO MAKE CAKE: In medium saucepan, combine butter, cola, and cocoa powder. Cook and stir over medium heat until butter melts. Pour over flour mixture. Add eggs, buttermilk, baking soda, and vanilla; mix well. Stir in marshmallows. Pour into prepared baking pan. Bake for 30 to 35 minutes or until a wooden toothpick inserted near center comes out clean. Cool cake in pan on wire rack.
Step 4: TO MAKE FROSTING: In medium bowl, beat 1/3 cup soft butter with electric mixer on medium to high speed for 30 seconds. Slowly add 1 3/4 cups powdered sugar and 2 tablespoons unsweetened cocoa powder, beating until combined. Add 1/4 cup cola, beating until combined. If necessary, beat in additional confectioners sugar and cola if needed to make frosting easy to spread.
Step 5: Spread Cocoa-Cola Frosting over cake. Sprinkle with pecans and marshmallows, if desired.