Bring to a boil:

1 c. butter
1 c. Coca Cola
3 tbsp. cocoa

Set aside. Put in mixing bowl and beat together:

1 3/4 c. sugar
2 c. flour
1 tsp. baking soda
2 eggs, slightly beaten
1/2 c. buttermilk (or 1/2 c. milk with 1 tsp. vinegar)
1 tsp. vanilla

Pour in the Coca-Cola mixture and blend well with mixer. By hand, stir in 1 1/2 cups miniature marshmallows. Bake in greased 9 x 13 inch pan in 350 degree oven for 40 to 50 minutes. When done, add the frosting while still warm.

FROSTING:

1/3 c. Coca-Cola
1/2 c. butter
3 tbsp. cocoa
3 1/2 c. powdered sugar

Heat Cola, butter and cocoa. Add powdered sugar. Beat until smooth.