Melt butter and cocoa over medium heat.
Remove from heat and stir in sugar.
Add eggs and mix well.
Add flour, salt and vanilla, stirring well.
Pour into a greased and floured 13"x 9"x 2" pan.
Bake in pre-heated 350 degree oven for 30 to 40 minutes.
Test after 30 minutes for doneness.
As soon as cake is removed from oven, sprinkle top with marshmallows.
Spread with chocolate frosting.
Mix all ingredients together until smooth.