6 ounces butter (3/4 cup, 1 1/2 sticks) 
1 1/2 cups sugar 
3 tablespoons unsweetened cocoa 
1 1/2 cups self-rising flour 
1 1/2 cups chopped pecans 
1 teaspoon vanilla extract 
6 ounces miniature marshmallows, about 3 cups 

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.

Icing 

1/4 cup butter 
1 lb confectioners sugar (about 3 1/2 cups unsifted) 
1/4 cup unsweetened cocoa 
1 teaspoon vanilla 
milk 

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.