6 ounces butter (3/4 cup, 1 1/2 sticks)
Cream butter and sugar until light and fluffy; beat in cocoa. Add eggs, one at a time, beating well after each addition. Add flour, nuts and vanilla; mix well. Pour batter into greased and floured 9x13x2-inch baking pan. Bake chocolate marshmallow cake at 325° for 40 minutes. Remove from oven and place miniature marshmallows on top of hot cake. Let marshmallows melt then frost with icing (below) while still warm.
1/4 cup butter
Mix all ingredients together, adding milk until desired spreading consistency is reached; spread on warm chocolate marshmallow cake. Cool chocolate marshmallow cake thoroughly before serving.